The pressure on Sharapova to hit clean winners is causing the Russian to overcook her shots, an adrenalised forehand sails over the baseline... 0-15. 

Williams closing in on victory, grabbing a 15-30 advantage, though Sharapova aims a serve to the rib cage to level at 30-30. 

The Russian with gravel for guts, two quick points, the forehand on song, and the bagel is at least avoided. Williams to serve for the match. 

It's all too easy for Williams now, a 11th ace takes her to 30-0. This match coming to the conclusion many would have predicted. 

It isn't a blemish-free hold for the top seed, there is a double fault and a simple forehand miss. Sharapova's famous fighting spirit keeping her in the game, forcing it to deuce. Williams with plenty left in the tank, though, a super serve sets up a thumping volley, and another ace wraps up the hold. 

Sharapova's intensity has dipped somewhat, as you'd perhaps expect it to when a set and a break down against an opponent she last beat in 2004. 

Williams ruthless from the back of the court, a flick of the wrist and a forehand zips by Sharapova for 15-30. 

Eek. A double fault. Two break points Williams. Empathetic encouragement for Sharapova from the crowd, but Williams is marching towards the semi-finals. The world number one breaks. She's now won 10 of the last 12 games. 

If history tells us anything - and it tells us Sharapova has only managed to win three sets in 17 matches against Williams - then the Russian is not going to stem the tide. Another love hold for Williams. 

Sharapova can't afford to let her form dip, to start thinking about the ifs and buts of the first set. Williams wins the opening point, but the Russian's response - a winning forehand into the corner - suggests she has plenty left to give. 

From 15-15 to 30-30. When Sharapova gets her first serves in, she manages to get the better of Williams, which she does on this occasion, constructing  the point brilliantly to beat her rival with a humdinger of a forehand. 

Worryingly though for Sharapova, Williams forces her to deuce and collects a break point as Sharapova nets. A backhand down the line from Williams and the game is hers. Williams just raises a clenched fist and stares with ferocity. Sharapova sends up an SOS flare. 

A super-duper hold to love for Williams so whatever was troubling her after the first set isn't hindering her serve. There's now a lot of pressure on Sharapova's shoulders. 

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A Doctor trots onto the court to chat with Williams. The top seed isn't receiving any treatment so perhaps was just seeking some advice. 

Their encounter is brief as the American is leaving her chair and is preparing to serve. Stand by, the second set is on its way. 

"Come on, Maria," yells an Aussie in the crowd as Sharapova faces a  fourth set point. 

First serve hits the target, promising, but Williams constructs the point beautifully, sending Sharapova out wide before pouncing at the net with an irretrievable volley.   

After 55 minutes, Williams has the first set in the bag. 

Oof! Take that, says Williams, as she punches a winning return down the line for a second set point. Sharapova on the ropes, as some would say, but the Russian is holding on as Williams fails to negotiate the barrier on the return. Deuce. 

Williams targeting the Sharapova backhand, stepping further and further towards the tape and the Russian, in an attempt to produce a swashbuckling winner, sends a backhand long. Third set point. 

What will Sharapova do next? A first serve to the forehand, another return to the net. Deuce. Will this game ever end? 

Here we are then, in the crucial stage of this set. Sharapova can't afford any blips, the double faults must stay away. 

But it doesn't really matter what Sharapova throws at Williams because the defending champ is returning with ferocity - two clean winners for a 0-30 lead. 

Sharapova launches two well-placed first serves, though, to haul herself back to 30-30, and the Russian comes out on top of the longest rally of the match. Williams can't quite believe Sharapova managed to retrieve her flame-throwers. 40-30. 

Williams forces her way to deuce courtesy of a fortuitous net cord. The top seed then ups the ante, collects a set point... but slaps a return into the net and Sharapova escapes. For now. 

A second break point comes Sharapova's way, a second break point is saved. Williams powers back from the brink, her serve coming to the rescue again, but Sharapova is refusing to yield. 

Break point. Deuce. Advantage. Deuce... Eight minutes elapse... Williams revved up, throws a vicious forehand at Sharapova to advance to advantage and concludes a significant hold with a thunderclap of an ace. 

Decibels rising inside Rod Laver Arena... Both players snarling. Winning points greeted with growls. There is beef between them, of course. 

But Williams even applauds a sumptuous backhand down the line winner from Sharapova as she levels at 15-15. 

A double fault from Williams this time. Interesting. Sharapova's power forcing Williams on the defensive, the top seed sent from tramline to tramline before Sharapova kills the point with a forehand winner. Deuce. 

Both players now struggling on the serve as a double fault from Williams gifts Sharapova a break point. Sharapova given no chance to take her chance, an ace saving Williams' bacon...

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Double faults still hindering Sharapova's game, a fifth presents Williams with the opening point. More second serves coming the American's way, too, which Williams greets with relish. The world number one 0-30 to the good... Danger... 

Oh my, another double fault and Williams has three break points which could effectively be regarded as set points. 

One saved, two saved... Sharapova's first serve cooking now... Another mighty effort required and she comes up with an ace! Bravo. To deuce we go. Sharapova has flicked on the switch... five points in a row, ending a remarkable hold with an equally remarkable angled forehand which kisses the tramline. 

Is there another way to greet a winning point than to yell "come on"? Seems not as it appears to be the go-to phrase for both Williams and Sharapova. How about "take that, punk", just for a bit of variety. 

Fabulous! A crackerjack backhand return from Sharapova to level at 30-30 but, unfortunately for the Russian, Williams can simply respond with a cool ace - her fifth of the match. 

Williams a point away from holding, a boomer down the T, Sharapova gets some graphite on it but there's no real hope of actually returning a ball which hurtles at such speed. 

A fourth double fault from Sharapova. She must stop the rot from setting in, and must do so quickly. It's only15-15, but the former champion is accumulating double faults with a tad too much frequency. The rest of the Russian's game, though, is sharp, which is why she pulls through to hold, celebrating with a "come on". 

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Williams serving with ruthless efficiency. A third ace of the match takes her to 30-0, though the sunlight continues to cause her some difficulty during the ball toss. 

Another ace lasered out wide, wrong-footing Sharapova, and the top seed marches to 40-15. Sharapova overcooking her shots, she has to do something when she has the chance, I suppose, and is ahead for the first time in this match. 

People still filtering into the arena, plenty of empty seats despite a cracker unfolding. Williams finding her groove, whacking a formidable forehand winner which Sharapova must watch fly by. 15-15. 

Another double fault from Sharapova allows Williams to level at 30-30, and another. Danger. Break point gifted to Williams. Sharapova should have just presented the ball to her opponent wrapped in a fancy ribbon. 

Williams pounces on the return, grabs the initiative in the rally, and Sharapova is forced wide. Parity is restored. 

Sharapova has started aggressively, adding plenty of power to her groundstrokes. A monster of a forehand pins the top seed into a coner and the Russian nips 15-30 ahead. She's not going to break again, surely? 

Perhaps. The pair must slug it out at deuce. Williams' serve though is a mighty weapon - boom  - an ace -  her second of the match - wraps up the hold. 

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Sharapova this term serving into the sunshine, the giant orb messing with the vision so the fifth seed takes her time with the ball toss. 

There's a hush on Rod Laver, the crowd wondering perhaps whether Sharapova can consolidate her advantage. Williams, as you expect, a little riled. "Come on," she snarls as she levels to 15-15. 

Sharapova, a little predictably perhaps, chucks in a double fault to give her opponent a slight advantage, though the Russian is coming out on top of the lengthier rallies. 30-30. 

A fine return from Williams, but she proceeds to slap a forehand into the tape... and Sharapova arrows an ace down the T to conclude a comfortable hold.