Right then, that's me done and dusted. Thanks, as ever, for your company. It's been an absolute pleasure.
Don't go too far, mind, as Britain's Andy Murray will be in action shortly. Aimee Lewis will be in the live text hot seat for that one, with his semi-final against Tomas Berdych kicking off at 08:30 GMT.
Until next time, it's good morning from me. Bye!
Post update
And news just in, Britain's Laura Robson is targeting a return to the WTA Tour in Indian Wells in March.
The 21-year-old, who has not played for over a year because of a left wrist injury, is on the entry list for the tournament in southern California.
Post update
So top seed Serena Williams will play second seed Maria Sharapova in Saturday's final. Williams has won the title five times and never lost a final in Melbourne. Sharapova has won the title once, in 2008, and reached two other finals.
Post update
EPACopyright: EPA
Williams has been struggling with a cold the last few days, but the American reports that she is feeling better. "I'm a lot better, every day gets better," she says. "Have a day off tomorrow so hopefully by Saturday I'll have recuperated."
Post update
Piers Newbery
BBC Sport at Melbourne Park
EPACopyright: EPA
"It was a more of a test than the scoreline might suggest but Williams did a superb job of coping with one of the very few players who can match her for power.
"With the pair averaging within 1km per hour of each other on serve, Williams managed to break three times while Keys failed to repeat her break of the very first game.
"The top seed will now take on the second seed with a record that is far more lopsided than their rankings would suggest - Williams leads Sharapova 16-2, with no defeats since 2004."
Post update
"She pushed me really hard in the first set and I had to dig deep mentally to get through that," says Williams who will play Maria Sharapova in the final.
"She came up with some great shots every time," adds the American with regards Keys saving seven match points on her serve. "I could have done a little more in terms of being aggressive, but it's a good sign she played so well when she's down - she never ever gave up."
Post update
EPACopyright: EPA
"I'm really excited to be in the final again," says Williams, who will contest her sixth Australian Open final. "I didn't come here with that expectation so it's really exciting.
"Madison is obviously a great player, she is going to be winning this tournament and lots of other Grand Slams very soon.
"I'm happy to see her do so well and be such a great sport at the same time."
Williams through to the final
Williams 7-6 (7-5) 6-2 Keys*
"Come on," roars Williams as she recovers from 0-15 to 30-15 with some brilliant serving. But she then takes something off her next effort and Keys takes advantage to level at 30-30.
A real impressive stretching backhand from Williams bring up her eighth match point - first on her own serve - but a blistering return almost knocks Williams off her feet as she tries and fails to get something on it. Deuce.
A ninth match point for Williams now - and she takes it with her 13th ace of the match.
Post update
*Williams 7-6 (7-5) 5-2 Keys
APCopyright: AP
Keys is battling bravely against a Williams onslaught and hangs on when the top seed gets her first match point to force deuce.
Williams conjures up a second, third, fourth, fifth and sixth match point, but Keys has an answer to everyone of them. She then chases down a forehand and whips it down the line for a winner and game point.
This is turning into a lengthy game as we head back to deuce. And deuce again. A seventh match point for Williams now, but Keys saves this one, too, dealing with a classy overhead.
There's a standing ovation as Keys wins the next two points to make Williams serve for the match. Her coach Lindsay Davenport, a former world number one, smiles and applauds from the stands.
Post update
Piers Newbery
BBC Sport at Melbourne Park
"Breaking news from the media centre - Lleyton Hewitt says: 'I plan to play the Aussie Open next year and most likely finish there.' It comes as Pat Rafter steps down as Australia Davis Cup captain to be replaced in the interim by Wally Masur, with Hewitt taking over 'when he's ready'. Rafter becomes director of performance for Tennis Australia next month and says he can't fill both roles.'"
Post update
Williams 7-6 (7-5) 5-1 Keys*
A love game for Williams and she is now just one away from a place in what will be her sixth Australian Open.
Williams breaks
*Williams 7-6 (7-5) 4-1 Keys
EPACopyright: EPA
Williams has the bit between her teeth right now - she really wants this - and attacks the Keys serve, earning two break points for her trouble.
Keys bravely fights back to deuce, but an error of the forehand and a double fault undoes her hard work. Williams breaks again. It'll be a long way back now for the young American...
Post update
Williams 7-6 (7-5) 3-1 Keys*
Williams fires a 120mph serve out wide to seal another service hold. Victory in this match will ensure she will remain at the top of the world rankings.
Post update
*Williams 7-6 (7-5) 2-1 Keys
Keys is bidding to become the first teenager to reach a Grand Slam final since Caroline Wozniacki achieved the feat at the 2009 US Open and she keeps herself in with a chance of doing so as she races through her service game to love.
Post update
Williams 7-6 (7-5) 2-0 Keys*
Supreme response from 19-year-old Keys, who looks at home on the big stage, as she rustles up two break points. Williams saves the first with an ace and is back to deuce when Keys hits a backhand wide.
Both players have served impressively throughout the match and that continues, Williams hitting her ninth ace to bring up game point. The game is hers when Keys' makes her 25th unforced errors. Williams has made just 11.
Williams breaks
*Williams 7-6 (7-5) 1-0 Keys
Getty ImagesCopyright: Getty Images
Nightmare for Keys as her forehand deserts her, the American teenager making four successive errors on that flank to hand Williams the break.
Game and first set
Williams 7-6 (7-5) Keys*
Keys goes big with a cross-court forehand but it drifts long and it's three set points for Williams. The unseeded 19-year-old saves the first two with two aces but Williams is jumping for joy as she watches a Keys' return drift long. The top seed wins the first the hard way in 45 minutes.
Tie-break
*Williams 6-6 (3-3) Keys
Williams steps up to the mark in the tie-break, the first both she and Keys have played in this tournament. The American gets the mini-break early on to lead 4-2 at the changeover.
Post update
*Williams 6-6 Keys
Getty ImagesCopyright: Getty Images
Keys races to 40-0 on serve but then gets caught out by the blustery conditions. The young American is unfazed, mind, firing her fifth ace of the match to win the game. Tie-break anyone?
Britwatch
Piers Newbery
BBC Sport at Melbourne Park
"News from court six, where British junior Katie Swan has made it through to the girls' semi-finals. The 15-year-old from Bristol but based in Kansas beat American Raveena Kinglsey 6-4 6-3, with Fed Cup captain Judy Murray watching from courtside. Swan, seeded 14th, will play Hungarian fifth seed Dalma Galfi in the last four."
Post update
Williams 6-5 Keys*
APCopyright: AP
A delicious lob, disguised beautifully, from Williams hauls the American back to 30-30. An 122mph ace - her fastest serve so far - brings up game point but Keys forces deuce with a backhand winner down the line.
But Williams clings on to win the next two points and seal the game. Keys to serve to stay in the set once more.
Post update
*Williams 5-5 Keys
Keys finds herself under a bit of pressure as Williams closes to 30-40, but deals with it well, firing an ace to seal the game and level the set.
Post update
Williams 5-4 Keys*
Every time Serena Williams has got past the quarter-finals in the Australian Open, she has gone on to win the title. The top seed puts herself into the driving seat to continue that streak with another solid service hold. You get the sense Williams is starting to get into her stride now...
Post update
Piers Newbery
BBC Sport at Melbourne Park
"All eyes in the media seats are trained on Keys' heavily strapped left thigh, with the odd murmur that we are starting to see signs of discomfort from the teenager. If she can keep getting that first serve in then she has a chance, having won 91% of the points behind it so far, but miss that and she's in trouble, winning a woeful 17% behind the second serve."
Post update
*Williams 4-4 Keys
Impressive response from Keys, the young American putting the disappointing of being broken back behind her with a comfortable service hold.
Post update
Williams 4-3 Keys*
APCopyright: AP
Williams races through her service game to love to move ahead for the first time in the match.
Williams breaks
*Williams 3-3 Keys
Madison Keys has looked like a world-class player for 15 minutes but the American shows her first sign that she can feel that left injury. She winces as she lands on it after a first serve.
Suddenly, she's facing two break points. Williams sends a tricky volley long to miss out on the first but is rewarded with the second as Key's backhand breaks down. Williams breaks.
Post update
Williams 2-3 Keys*
A better start from Williams in this service game, the American opening with a winner before cruising to 40-0. Keys hits back in the next two points but then fires wide to concede the game.
Post update
*Williams 1-3 Keys
Keys' hitting heavy off both flanks at the moment and her serve is working beautifully, too. The result is another easy service game.
Post update
Williams 1-2 Keys*
Williams, who has been struggling with a cold for a few days now, doesn't look to quick on her feet at the moment. But nonetheless, the top seed summons some fine first serves and closes out her service game with an ace to get on the board.
Post update
*Williams 0-2 Keys
Keys' left thigh is heavily strapped, the American requiring a medical timeout during her victory over Venus Williams in the previous round. But it doesn't look like it's causing her any problems as she races through her first service game to consolidate the break.
Keys breaks
Williams 0-1 Keys* (*denotes the next to serve)
Madison Keys is playing in her first Grand Slam semi-final - but you wouldn't know that based on her start in this game. The 19-year-old batters the Williams serve early on to carve out an opening at 0-30.
Williams recovers to 30-30 with an ace, but gifts her opponent a break point with a backhand error and then throws in another to concede the game. Keys off to a flier.
Post update
Piers Newbery
BBC Sport at Melbourne Park
"Madison Keys steps into the Grand Slam spotlight for real today, but she made her first breakthrough in the more sedate surroundings of Eastbourne last summer. The teenager won her first WTA title at Devonshire Park, the perfect place to get some experience of playing tennis in the wind. It was also where she picked up the thigh injury that forced her to retire at Wimbledon, and resurfaced in her semi-final win over Venus Williams on Tuesday."
Post update
The warm-up is over. Serena Williams will be the first to serve. Let's play tennis.
Post update
ReutersCopyright: Reuters
Madison Keys, 19, is going for a rare Williams-Williams double, taking on Serena after beating Venus in the quarter-finals. If she achieves the feat, she will be only the eighth player to beat both Williams sisters at the same tournament.
Post update
Right, then. Ready for a second semi-final? Good, because we've got one coming up. After an all-Russian encounter, we have an all-American match-up - top seed Serena Williams v unseeded Madison Keys.
Post update
Getty ImagesCopyright: Getty Images
Victory for Sharapova keeps alive her hopes of snatching the number one ranking from Serena Williams. The Russian needs to win the Australian Open and hope Williams loses to Madison Keys.
Post update
Piers Newbery
BBC Sport at Melbourne Park
"Coach Sven Groeneveld is up on his feet along with the rest of Team Maria, decked out in blue tops and baseball caps and looking not unlike a patrol of UN peacekeepers. The Dutchman has certainly played a big part in keeping Sharapova at the very top of the sport after serious shoulder problems. 'She's not known for her defence but it's improved so much,' says 18-time Grand Slam champion Chris Evert on ESPN. 'I never thought I'd see the day when Maria Sharapova was flying around the baseline.'"
Game, set and match
Sharapova 6-3 6-1 Makarova
Sharapova races to 40-15 and then watches on as Makarova's backhand lets her down again. The Russian second seed and 2008 Australian Open champion is through to her fourth final at Melbourne Park. She'll play Serena Williams or Madison Keys, who will be on-court shortly in the second semi-final.
Post update
*Sharapova 6-3 5-2 Makarova
Makarova scrapes through her service game for only her second hold of the set, but you get the feeling it is only delaying the inevitable. Sharapova to serve for a place in the final.
Post update
Sharapova 6-3 5-1 Makarova*
It looked like Makarova didn't have an alternative to a gameplan of trying to out-hit Sharapova, which isn't working, but perhaps she does.
The 11th seed takes a little off her groundstrokes to keep the ball in play, but remains aggressive by coming to the net. A couple of double faults from Sharapova and Makarova is rewarded with two breaks points.
However, Sharapova has no intention of staying out here longer than she has to, bringing up deuce with an ace. Makarova throws in two more errors and concedes the game. She will now serve to stay in the match.
Post update
*Sharapova 6-3 4-1 Makarova
EPACopyright: EPA
Some respite for Makarova as she moves to 40-0 with relative ease and though Sharapova takes the next two points with some big, big hitting, the second seed's forehand then lets her down. Makarova is on the board in this set.
Post update
Piers Newbery
BBC Sport at Melbourne Park
"News of the all-US contest coming up next - Serena Williams has been seen hitting freely on the outside courts this morning, with no sign of the coughing fits that have afflicted her in recent days, while Madison Keys chose to hit indoors. Her troublesome thigh was heavily strapped, but ESPN report she was smiling at the end and said she felt 'better than yesterday'."
Post update
Sharapova 6-3 4-0 Makarova*
When Makarova's forehand works, it's a very handy weapon. The Russian fires a forehand deep into the corner and follows it up with a sizzler down the line for 0-15. Unfortunately, we've not seen enough of it today.
Still, she has a chance at 0-30 courtesy of a Sharapova double-fault only to throw it away with three successive unforced errors. Sharapova then closes out the game with an ace to move just two games away from the final.
Sharapova breaks
*Sharapova 6-3 3-0 Makarova
Getty ImagesCopyright: Getty Images
The longer the rally, the less likely it is that Makarova will win it. The 11th seed is struggling with the depth and placement of her groundstrokes and Sharapova is taking advantage.
Makarova fires long to gift Sharapova a break point and she takes it with a backhand cross-court volley. It'll be along way back for Makarova now if she is to turn it around.
Post update
Sharapova 6-3 2-0 Makarova*
Sharapova throws in her fourth double fault of the match as Makarova closes to 40-30, but the 11th seed sprays another forehand out of court and Sharapova consolidates the break.
"Sharapova deserved the first set for the stunning sequence of returns she put together in the eighth game, just as the set had looked as if it was back in the balance. She looks in the mood, and hardly ever loses to other Russians these days."
Sharapova breaks
*Sharapova 6-3 1-0 Makarova
Oh dear. The first game of the second set has not gone well for Makarova, whose unforced error count has rocketed to 17. The 11th seed is broken for the third time in the match.
Post update
Piers Newbery
BBC Sport at Melbourne Park
"Sharapova wins eight of the last nine points to take the set, finally getting over those serving glitches in the gusting wind. Makarova has simply not been able to punish the most vulnerable part of Sharapova's game, winning just 27% of points on the former champion's second serve. Give Sharapova the chance to set her feet and swing and there are few to rival her - 15 winners to five making the difference."
Game and first set
Sharapova 6-3 Makarova*
Ruthless stuff from Sharapova who races through a love service game to clinch the first set. Makarova needs to get Sharapova on the run, because her compatriot is dictating the play all too easily.
Sharapova breaks
*Sharapova 5-3 Makarova
Getty ImagesCopyright: Getty Images
Sharapova gave herself a stern talking to at the end of that last game and it seems to have done the trick.
After losing the first point, the Russian goes on the attack, battering the Makarova serve and hitting four clean winners to break again. She will now serve for the set.
Makarova breaks
Sharapova 4-3 Makarova*
Better from Makarova, the 11th seed stepping inside the baseline to attack a forehand and gain a sniff of a chance at 15-30. Sharapova then gift-wrap's two break points with an untimely double-fault.
The first goes wanting, Makarova just snatching at backhand but she is successful second time round as Sharapova dumps a forehand in the net. "Come on," roars Makarova in the direction of her box. Sloppy from Sharapova and we're back on serve.
Post update
*Sharapova 4-2 Makarova
Flashes of form from Makarova, the Russian connecting perfectly with a forehand that sizzles down the line for 30-15. But she soon finds herself at deuce, as she has done in both her service games so far.
Break point for Sharapova, the second seed punishing another short ball with a textbook forehand down the line. But Makarova's serve comes to the rescue and she comes through as Sharapova fires wide. Makarova is hanging on to her compatriots coattails, just.
Post update
Sharapova 4-1 Makarova*
APCopyright: AP
Sharapova is starting to motor now, the Russian cruising through her service game for the loss of just a single point and that lengthy first game is now a thing of the past.
Post update
Piers Newbery
BBC Sport at Melbourne Park
"Speaking of Russian tennis, the Fed Cup team for next month's clash against Poland and the Radwanskas has been announced. It will be led by Sharapova, causing much interest as the world number two has only ever represented her country three times in the event. Makarova is not involved and the captain is the aforementioned Anastasia Myskina, the former French Open champion (who had a 3-2 record against Sharapova)."
Post update
*Sharapova 3-1 Makarova
Makarova's first serve looks very ropey at the moment, the ball sitting up and just asking to be hit. Sharapova obliges and earns herself two break points after her opponent dumps a forehand in the net.
At last, the 11th seed finds a couple of big serves to bring up deuce and despite facing a couple more break points, Makarova grinds out the game and gets herself on the board. That should help the nerves.
Post update
Sharapova 3-0 Makarova*
Sharapova has won 21 of her last 22 matches against Russians, a stretch that dates back to the start of the 2011 season.
And it looks like the five-time Grand Slam champion wants to wrap up a 22nd victory in super-quick time after that first game blip.
The second seed races through her service game to love. Makarova needs to find some form - and quick.
If you were wondering what the only loss in that run was, it came against Anastasia Pavlyuchenkova at the Paris Indoors last year.
Sharapova breaks
*Sharapova 2-0 Makarova
It's another lengthy game, with Makarova now coming under pressure on serve, the Russian shanking a backhand to bring up deuce.
Sharapova piles on the pressure and while a return drifts just long on a first break point, she makes no mistake on her next opportunity, hammering a short ball down the line for a forehand winner.
Cue clenched fist and a shriek of "come on". Sharapova breaks and after the hopeful start in the first game, Makarova now finds herself on the ropes.
Post update
Sharapova 1-0 Makarova* (*denotes the next to serve)
It's pretty breezy out on Rod Laver and it's clear Sharapova isn't enjoying the conditions, the Russian struggling with her ball toss and immediately facing a couple of break points after being hauled to deuce.
It's not pretty, but somehow, Sharapova digs herself out of trouble and comes through a 10-minute game. We could be here some time, folks...
Post update
The umpire is ready. The players are ready. Are you ready? Good. Let's play tennis.
Post update
Makarova wins the toss and chooses to receive. We're minutes away, folks.
Post update
The players have strolled out on court, wearing varying shades of neon orange.
The crowd on Rod Laver Arena were treated to a deciding set in the first match of the day, with Jean-Julien Rojer and Horia Tecau winning their men's doubles semi-final.
Will they get the same again in this all-Russian last four encounter?
Post update
Piers Newbery
BBC Sport at Melbourne Park
"It's bright and breezy - it's always breezy at Melbourne Park - 19C, and the growing sense of anticipation mingled with the aroma of deep fried chicken products tells us that the crowd is making final preparations for a big day ahead.
British eyes might sneak a look at Court Six soon, where Katie Swan will play her junior quarter-final, and the 15-year-old from Bristol has named Sharapova among her tennis idols.
Well, the woman herself is about to get under way now the doubles have finished on Rod Laver Arena in the first all-Russian Grand Slam semi-final since Dinara Safina beat Vera Zvonareva here six years ago."
Post update
EPACopyright: EPA
Ekaterina Makarova, the 10th seed, is in impressive form, returning to the top 10 for the first time earlier this year.
The Russian has won all her matches in Melbourne in straight sets and for the loss of just 27 games.
This is her second Grand Slam semi-final, after making the last four at the US Open last year. Can she trouble Sharapova, a five-time Grand Slam champion?
Post update
Piers Newbery
BBC Sport at Melbourne Park
"A lot of the focus has been on the Williams sisters and bright new American hope Madison Keys, but this is a big day for Russian tennis. With the likes of Anastasia Myskina, Elena Dementieva and Dinara Safina long gone, Maria Sharapova has remained the nation's leading light - albeit one based in Florida. Ekaterina Makarova was asked after her quarter-final whether her illustrious compatriot "feels different" to the other Russian players. 'That's a tough question,' she said. 'I just want to leave it.'"
Post update
Getty ImagesCopyright: Getty Images
There's no doubt Maria Sharapova wants this. Since her one and only Australian Open title back in 2008, the Russian has only won two Grand Slams.
But today, she stands just one match away from a fourth final at Melbourne Park and a potential match-up with top seed Serena Williams.
Victory, too, will see her remain in the hunt to regain the world number one status. Standing in her way is compatriot Ekaterina Makarova, who has never beaten the second seed in five attempts. Will it be sixth time lucky?
Live Reporting
Lawrence Barretto
All times stated are UK
Get involved
Getty ImagesCopyright: Getty Images 
EPACopyright: EPA 
EPACopyright: EPA 
EPACopyright: EPA 
APCopyright: AP 
EPACopyright: EPA 
Getty ImagesCopyright: Getty Images 
Getty ImagesCopyright: Getty Images 
APCopyright: AP 
APCopyright: AP 
ReutersCopyright: Reuters 
Getty ImagesCopyright: Getty Images 
EPACopyright: EPA 
Getty ImagesCopyright: Getty Images 
Getty ImagesCopyright: Getty Images 
APCopyright: AP 
EPACopyright: EPA 
Getty ImagesCopyright: Getty Images
Latest PostPost update
Right then, that's me done and dusted. Thanks, as ever, for your company. It's been an absolute pleasure.
Don't go too far, mind, as Britain's Andy Murray will be in action shortly. Aimee Lewis will be in the live text hot seat for that one, with his semi-final against Tomas Berdych kicking off at 08:30 GMT.
Until next time, it's good morning from me. Bye!
Post update
And news just in, Britain's Laura Robson is targeting a return to the WTA Tour in Indian Wells in March.
The 21-year-old, who has not played for over a year because of a left wrist injury, is on the entry list for the tournament in southern California.
Post update
So top seed Serena Williams will play second seed Maria Sharapova in Saturday's final. Williams has won the title five times and never lost a final in Melbourne. Sharapova has won the title once, in 2008, and reached two other finals.
Post update
Williams has been struggling with a cold the last few days, but the American reports that she is feeling better. "I'm a lot better, every day gets better," she says. "Have a day off tomorrow so hopefully by Saturday I'll have recuperated."
Post update
Piers Newbery
BBC Sport at Melbourne Park
"It was a more of a test than the scoreline might suggest but Williams did a superb job of coping with one of the very few players who can match her for power.
"With the pair averaging within 1km per hour of each other on serve, Williams managed to break three times while Keys failed to repeat her break of the very first game.
"The top seed will now take on the second seed with a record that is far more lopsided than their rankings would suggest - Williams leads Sharapova 16-2, with no defeats since 2004."
Post update
"She pushed me really hard in the first set and I had to dig deep mentally to get through that," says Williams who will play Maria Sharapova in the final.
"She came up with some great shots every time," adds the American with regards Keys saving seven match points on her serve. "I could have done a little more in terms of being aggressive, but it's a good sign she played so well when she's down - she never ever gave up."
Post update
"I'm really excited to be in the final again," says Williams, who will contest her sixth Australian Open final. "I didn't come here with that expectation so it's really exciting.
"Madison is obviously a great player, she is going to be winning this tournament and lots of other Grand Slams very soon.
"I'm happy to see her do so well and be such a great sport at the same time."
Williams through to the final
Williams 7-6 (7-5) 6-2 Keys*
"Come on," roars Williams as she recovers from 0-15 to 30-15 with some brilliant serving. But she then takes something off her next effort and Keys takes advantage to level at 30-30.
A real impressive stretching backhand from Williams bring up her eighth match point - first on her own serve - but a blistering return almost knocks Williams off her feet as she tries and fails to get something on it. Deuce.
A ninth match point for Williams now - and she takes it with her 13th ace of the match.
Post update
*Williams 7-6 (7-5) 5-2 Keys
Keys is battling bravely against a Williams onslaught and hangs on when the top seed gets her first match point to force deuce.
Williams conjures up a second, third, fourth, fifth and sixth match point, but Keys has an answer to everyone of them. She then chases down a forehand and whips it down the line for a winner and game point.
This is turning into a lengthy game as we head back to deuce. And deuce again. A seventh match point for Williams now, but Keys saves this one, too, dealing with a classy overhead.
There's a standing ovation as Keys wins the next two points to make Williams serve for the match. Her coach Lindsay Davenport, a former world number one, smiles and applauds from the stands.
Post update
Piers Newbery
BBC Sport at Melbourne Park
"Breaking news from the media centre - Lleyton Hewitt says: 'I plan to play the Aussie Open next year and most likely finish there.' It comes as Pat Rafter steps down as Australia Davis Cup captain to be replaced in the interim by Wally Masur, with Hewitt taking over 'when he's ready'. Rafter becomes director of performance for Tennis Australia next month and says he can't fill both roles.'"
Post update
Williams 7-6 (7-5) 5-1 Keys*
A love game for Williams and she is now just one away from a place in what will be her sixth Australian Open.
Williams breaks
*Williams 7-6 (7-5) 4-1 Keys
Williams has the bit between her teeth right now - she really wants this - and attacks the Keys serve, earning two break points for her trouble.
Keys bravely fights back to deuce, but an error of the forehand and a double fault undoes her hard work. Williams breaks again. It'll be a long way back now for the young American...
Post update
Williams 7-6 (7-5) 3-1 Keys*
Williams fires a 120mph serve out wide to seal another service hold. Victory in this match will ensure she will remain at the top of the world rankings.
Post update
*Williams 7-6 (7-5) 2-1 Keys
Keys is bidding to become the first teenager to reach a Grand Slam final since Caroline Wozniacki achieved the feat at the 2009 US Open and she keeps herself in with a chance of doing so as she races through her service game to love.
Post update
Williams 7-6 (7-5) 2-0 Keys*
Supreme response from 19-year-old Keys, who looks at home on the big stage, as she rustles up two break points. Williams saves the first with an ace and is back to deuce when Keys hits a backhand wide.
Both players have served impressively throughout the match and that continues, Williams hitting her ninth ace to bring up game point. The game is hers when Keys' makes her 25th unforced errors. Williams has made just 11.
Williams breaks
*Williams 7-6 (7-5) 1-0 Keys
Nightmare for Keys as her forehand deserts her, the American teenager making four successive errors on that flank to hand Williams the break.
Game and first set
Williams 7-6 (7-5) Keys*
Keys goes big with a cross-court forehand but it drifts long and it's three set points for Williams. The unseeded 19-year-old saves the first two with two aces but Williams is jumping for joy as she watches a Keys' return drift long. The top seed wins the first the hard way in 45 minutes.
Tie-break
*Williams 6-6 (3-3) Keys
Williams steps up to the mark in the tie-break, the first both she and Keys have played in this tournament. The American gets the mini-break early on to lead 4-2 at the changeover.
Post update
*Williams 6-6 Keys
Keys races to 40-0 on serve but then gets caught out by the blustery conditions. The young American is unfazed, mind, firing her fifth ace of the match to win the game. Tie-break anyone?
Britwatch
Piers Newbery
BBC Sport at Melbourne Park
"News from court six, where British junior Katie Swan has made it through to the girls' semi-finals. The 15-year-old from Bristol but based in Kansas beat American Raveena Kinglsey 6-4 6-3, with Fed Cup captain Judy Murray watching from courtside. Swan, seeded 14th, will play Hungarian fifth seed Dalma Galfi in the last four."
Post update
Williams 6-5 Keys*
A delicious lob, disguised beautifully, from Williams hauls the American back to 30-30. An 122mph ace - her fastest serve so far - brings up game point but Keys forces deuce with a backhand winner down the line.
But Williams clings on to win the next two points and seal the game. Keys to serve to stay in the set once more.
Post update
*Williams 5-5 Keys
Keys finds herself under a bit of pressure as Williams closes to 30-40, but deals with it well, firing an ace to seal the game and level the set.
Post update
Williams 5-4 Keys*
Every time Serena Williams has got past the quarter-finals in the Australian Open, she has gone on to win the title. The top seed puts herself into the driving seat to continue that streak with another solid service hold. You get the sense Williams is starting to get into her stride now...
Post update
Piers Newbery
BBC Sport at Melbourne Park
"All eyes in the media seats are trained on Keys' heavily strapped left thigh, with the odd murmur that we are starting to see signs of discomfort from the teenager. If she can keep getting that first serve in then she has a chance, having won 91% of the points behind it so far, but miss that and she's in trouble, winning a woeful 17% behind the second serve."
Post update
*Williams 4-4 Keys
Impressive response from Keys, the young American putting the disappointing of being broken back behind her with a comfortable service hold.
Post update
Williams 4-3 Keys*
Williams races through her service game to love to move ahead for the first time in the match.
Williams breaks
*Williams 3-3 Keys
Madison Keys has looked like a world-class player for 15 minutes but the American shows her first sign that she can feel that left injury. She winces as she lands on it after a first serve.
Suddenly, she's facing two break points. Williams sends a tricky volley long to miss out on the first but is rewarded with the second as Key's backhand breaks down. Williams breaks.
Post update
Williams 2-3 Keys*
A better start from Williams in this service game, the American opening with a winner before cruising to 40-0. Keys hits back in the next two points but then fires wide to concede the game.
Post update
*Williams 1-3 Keys
Keys' hitting heavy off both flanks at the moment and her serve is working beautifully, too. The result is another easy service game.
Post update
Williams 1-2 Keys*
Williams, who has been struggling with a cold for a few days now, doesn't look to quick on her feet at the moment. But nonetheless, the top seed summons some fine first serves and closes out her service game with an ace to get on the board.
Post update
*Williams 0-2 Keys
Keys' left thigh is heavily strapped, the American requiring a medical timeout during her victory over Venus Williams in the previous round. But it doesn't look like it's causing her any problems as she races through her first service game to consolidate the break.
Keys breaks
Williams 0-1 Keys* (*denotes the next to serve)
Madison Keys is playing in her first Grand Slam semi-final - but you wouldn't know that based on her start in this game. The 19-year-old batters the Williams serve early on to carve out an opening at 0-30.
Williams recovers to 30-30 with an ace, but gifts her opponent a break point with a backhand error and then throws in another to concede the game. Keys off to a flier.
Post update
Piers Newbery
BBC Sport at Melbourne Park
"Madison Keys steps into the Grand Slam spotlight for real today, but she made her first breakthrough in the more sedate surroundings of Eastbourne last summer. The teenager won her first WTA title at Devonshire Park, the perfect place to get some experience of playing tennis in the wind. It was also where she picked up the thigh injury that forced her to retire at Wimbledon, and resurfaced in her semi-final win over Venus Williams on Tuesday."
Post update
The warm-up is over. Serena Williams will be the first to serve. Let's play tennis.
Post update
Madison Keys, 19, is going for a rare Williams-Williams double, taking on Serena after beating Venus in the quarter-finals. If she achieves the feat, she will be only the eighth player to beat both Williams sisters at the same tournament.
Post update
Right, then. Ready for a second semi-final? Good, because we've got one coming up. After an all-Russian encounter, we have an all-American match-up - top seed Serena Williams v unseeded Madison Keys.
Post update
Victory for Sharapova keeps alive her hopes of snatching the number one ranking from Serena Williams. The Russian needs to win the Australian Open and hope Williams loses to Madison Keys.
Post update
Piers Newbery
BBC Sport at Melbourne Park
"Coach Sven Groeneveld is up on his feet along with the rest of Team Maria, decked out in blue tops and baseball caps and looking not unlike a patrol of UN peacekeepers. The Dutchman has certainly played a big part in keeping Sharapova at the very top of the sport after serious shoulder problems. 'She's not known for her defence but it's improved so much,' says 18-time Grand Slam champion Chris Evert on ESPN. 'I never thought I'd see the day when Maria Sharapova was flying around the baseline.'"
Game, set and match
Sharapova 6-3 6-1 Makarova
Sharapova races to 40-15 and then watches on as Makarova's backhand lets her down again. The Russian second seed and 2008 Australian Open champion is through to her fourth final at Melbourne Park. She'll play Serena Williams or Madison Keys, who will be on-court shortly in the second semi-final.
Post update
*Sharapova 6-3 5-2 Makarova
Makarova scrapes through her service game for only her second hold of the set, but you get the feeling it is only delaying the inevitable. Sharapova to serve for a place in the final.
Post update
Sharapova 6-3 5-1 Makarova*
It looked like Makarova didn't have an alternative to a gameplan of trying to out-hit Sharapova, which isn't working, but perhaps she does.
The 11th seed takes a little off her groundstrokes to keep the ball in play, but remains aggressive by coming to the net. A couple of double faults from Sharapova and Makarova is rewarded with two breaks points.
However, Sharapova has no intention of staying out here longer than she has to, bringing up deuce with an ace. Makarova throws in two more errors and concedes the game. She will now serve to stay in the match.
Post update
*Sharapova 6-3 4-1 Makarova
Some respite for Makarova as she moves to 40-0 with relative ease and though Sharapova takes the next two points with some big, big hitting, the second seed's forehand then lets her down. Makarova is on the board in this set.
Post update
Piers Newbery
BBC Sport at Melbourne Park
"News of the all-US contest coming up next - Serena Williams has been seen hitting freely on the outside courts this morning, with no sign of the coughing fits that have afflicted her in recent days, while Madison Keys chose to hit indoors. Her troublesome thigh was heavily strapped, but ESPN report she was smiling at the end and said she felt 'better than yesterday'."
Post update
Sharapova 6-3 4-0 Makarova*
When Makarova's forehand works, it's a very handy weapon. The Russian fires a forehand deep into the corner and follows it up with a sizzler down the line for 0-15. Unfortunately, we've not seen enough of it today.
Still, she has a chance at 0-30 courtesy of a Sharapova double-fault only to throw it away with three successive unforced errors. Sharapova then closes out the game with an ace to move just two games away from the final.
Sharapova breaks
*Sharapova 6-3 3-0 Makarova
The longer the rally, the less likely it is that Makarova will win it. The 11th seed is struggling with the depth and placement of her groundstrokes and Sharapova is taking advantage.
Makarova fires long to gift Sharapova a break point and she takes it with a backhand cross-court volley. It'll be along way back for Makarova now if she is to turn it around.
Post update
Sharapova 6-3 2-0 Makarova*
Sharapova throws in her fourth double fault of the match as Makarova closes to 40-30, but the 11th seed sprays another forehand out of court and Sharapova consolidates the break.
Post update
Russell Fuller
BBC tennis correspondent on Radio 5 live sports extra
"Sharapova deserved the first set for the stunning sequence of returns she put together in the eighth game, just as the set had looked as if it was back in the balance. She looks in the mood, and hardly ever loses to other Russians these days."
Sharapova breaks
*Sharapova 6-3 1-0 Makarova
Oh dear. The first game of the second set has not gone well for Makarova, whose unforced error count has rocketed to 17. The 11th seed is broken for the third time in the match.
Post update
Piers Newbery
BBC Sport at Melbourne Park
"Sharapova wins eight of the last nine points to take the set, finally getting over those serving glitches in the gusting wind. Makarova has simply not been able to punish the most vulnerable part of Sharapova's game, winning just 27% of points on the former champion's second serve. Give Sharapova the chance to set her feet and swing and there are few to rival her - 15 winners to five making the difference."
Game and first set
Sharapova 6-3 Makarova*
Ruthless stuff from Sharapova who races through a love service game to clinch the first set. Makarova needs to get Sharapova on the run, because her compatriot is dictating the play all too easily.
Sharapova breaks
*Sharapova 5-3 Makarova
Sharapova gave herself a stern talking to at the end of that last game and it seems to have done the trick.
After losing the first point, the Russian goes on the attack, battering the Makarova serve and hitting four clean winners to break again. She will now serve for the set.
Makarova breaks
Sharapova 4-3 Makarova*
Better from Makarova, the 11th seed stepping inside the baseline to attack a forehand and gain a sniff of a chance at 15-30. Sharapova then gift-wrap's two break points with an untimely double-fault.
The first goes wanting, Makarova just snatching at backhand but she is successful second time round as Sharapova dumps a forehand in the net. "Come on," roars Makarova in the direction of her box. Sloppy from Sharapova and we're back on serve.
Post update
*Sharapova 4-2 Makarova
Flashes of form from Makarova, the Russian connecting perfectly with a forehand that sizzles down the line for 30-15. But she soon finds herself at deuce, as she has done in both her service games so far.
Break point for Sharapova, the second seed punishing another short ball with a textbook forehand down the line. But Makarova's serve comes to the rescue and she comes through as Sharapova fires wide. Makarova is hanging on to her compatriots coattails, just.
Post update
Sharapova 4-1 Makarova*
Sharapova is starting to motor now, the Russian cruising through her service game for the loss of just a single point and that lengthy first game is now a thing of the past.
Post update
Piers Newbery
BBC Sport at Melbourne Park
"Speaking of Russian tennis, the Fed Cup team for next month's clash against Poland and the Radwanskas has been announced. It will be led by Sharapova, causing much interest as the world number two has only ever represented her country three times in the event. Makarova is not involved and the captain is the aforementioned Anastasia Myskina, the former French Open champion (who had a 3-2 record against Sharapova)."
Post update
*Sharapova 3-1 Makarova
Makarova's first serve looks very ropey at the moment, the ball sitting up and just asking to be hit. Sharapova obliges and earns herself two break points after her opponent dumps a forehand in the net.
At last, the 11th seed finds a couple of big serves to bring up deuce and despite facing a couple more break points, Makarova grinds out the game and gets herself on the board. That should help the nerves.
Post update
Sharapova 3-0 Makarova*
Sharapova has won 21 of her last 22 matches against Russians, a stretch that dates back to the start of the 2011 season.
And it looks like the five-time Grand Slam champion wants to wrap up a 22nd victory in super-quick time after that first game blip.
The second seed races through her service game to love. Makarova needs to find some form - and quick.
If you were wondering what the only loss in that run was, it came against Anastasia Pavlyuchenkova at the Paris Indoors last year.
Sharapova breaks
*Sharapova 2-0 Makarova
It's another lengthy game, with Makarova now coming under pressure on serve, the Russian shanking a backhand to bring up deuce.
Sharapova piles on the pressure and while a return drifts just long on a first break point, she makes no mistake on her next opportunity, hammering a short ball down the line for a forehand winner.
Cue clenched fist and a shriek of "come on". Sharapova breaks and after the hopeful start in the first game, Makarova now finds herself on the ropes.
Post update
Sharapova 1-0 Makarova* (*denotes the next to serve)
It's pretty breezy out on Rod Laver and it's clear Sharapova isn't enjoying the conditions, the Russian struggling with her ball toss and immediately facing a couple of break points after being hauled to deuce.
It's not pretty, but somehow, Sharapova digs herself out of trouble and comes through a 10-minute game. We could be here some time, folks...
Post update
The umpire is ready. The players are ready. Are you ready? Good. Let's play tennis.
Post update
Makarova wins the toss and chooses to receive. We're minutes away, folks.
Post update
The players have strolled out on court, wearing varying shades of neon orange.
The crowd on Rod Laver Arena were treated to a deciding set in the first match of the day, with Jean-Julien Rojer and Horia Tecau winning their men's doubles semi-final.
Will they get the same again in this all-Russian last four encounter?
Post update
Piers Newbery
BBC Sport at Melbourne Park
"It's bright and breezy - it's always breezy at Melbourne Park - 19C, and the growing sense of anticipation mingled with the aroma of deep fried chicken products tells us that the crowd is making final preparations for a big day ahead.
British eyes might sneak a look at Court Six soon, where Katie Swan will play her junior quarter-final, and the 15-year-old from Bristol has named Sharapova among her tennis idols.
Well, the woman herself is about to get under way now the doubles have finished on Rod Laver Arena in the first all-Russian Grand Slam semi-final since Dinara Safina beat Vera Zvonareva here six years ago."
Post update
Ekaterina Makarova, the 10th seed, is in impressive form, returning to the top 10 for the first time earlier this year.
The Russian has won all her matches in Melbourne in straight sets and for the loss of just 27 games.
This is her second Grand Slam semi-final, after making the last four at the US Open last year. Can she trouble Sharapova, a five-time Grand Slam champion?
Post update
Piers Newbery
BBC Sport at Melbourne Park
"A lot of the focus has been on the Williams sisters and bright new American hope Madison Keys, but this is a big day for Russian tennis. With the likes of Anastasia Myskina, Elena Dementieva and Dinara Safina long gone, Maria Sharapova has remained the nation's leading light - albeit one based in Florida. Ekaterina Makarova was asked after her quarter-final whether her illustrious compatriot "feels different" to the other Russian players. 'That's a tough question,' she said. 'I just want to leave it.'"
Post update
There's no doubt Maria Sharapova wants this. Since her one and only Australian Open title back in 2008, the Russian has only won two Grand Slams.
But today, she stands just one match away from a fourth final at Melbourne Park and a potential match-up with top seed Serena Williams.
Victory, too, will see her remain in the hunt to regain the world number one status. Standing in her way is compatriot Ekaterina Makarova, who has never beaten the second seed in five attempts. Will it be sixth time lucky?