Novak Djokovic beats Carlos Alcaraz 4-6 6-4 6-3 6-4 to reach semi-finals
Aryna Sabalenka survives huge scare to beat Anastasia Pavlyuchenkova and reach semi-finals
Paula Badosa earlier stuns Coco Gauff in 'dream come true' moment
Alexander Zverev sees off Tommy Paul to reach last four
Djokovic 4-6 3-2 Alcaraz*
Annabel Croft
Former British number one on BBC Radio 5 Live and BBC Sounds
The tempo that Alcaraz is playing at is just extraordinary.
Everything is coming at Djokovic thick and fast, and he hasn't got much time to react to anything.
You can feel the pressure he is under.
Djokovic 4-6 3-2 Alcaraz*
Novak Djokovic comes into the net but puts his volley wide and Carlos Alcaraz breaks back.
Another grimace from Djokovic tells you those fitness issues are likely still bothering him.
Image source, Reuters*Djokovic 4-6 3-1 Alcaraz
Novak Djokovic finds himself in a spot of bother by missing a couple of forehands and he closes his eyes in a look of frustration.
Carlos Alcaraz now has a disagreement with the umpire over what he deemed a late 'let' call.
A long forehand from Djokovic offers break point to Alcaraz.
*Djokovic 4-6 3-1 Alcaraz
Carlos Alcaraz powers through a rapid service game to hold to love.
Can he put some pressure back on Novak Djokovic's serve?
Djokovic 4-6 3-0 Alcaraz*
Novak Djokovic lands a big first serve before outplaying Carlos Alcaraz to hold.
If the Serb is struggling physically you wouldn't be able to tell from his form at the start of this second set.
*Djokovic 4-6 2-0 Alcaraz
Novak Djokovic goes for the serve and volley to great effect as he recovers from 0-15 down.
Carlos Alcaraz shows superb defence as a high lob wins him a point which looked lost, before Djokovic puts a forehand into the net for deuce.
You can't count Alcaraz out of any point.
*Djokovic 4-6 2-0 Alcaraz
Annabel Croft
Former British number one on BBC Radio 5 Live and BBC Sounds
Well that's got the crowd excited!
Don't forget, Novak Djokovic got that break in the first set. He has still got to really focus on this next service game to try to back it up now.
*Djokovic 4-6 2-0 Alcaraz
Break point for Novak Djokovic as the Serb crashes his third return winner of the game.
And he makes it count as Carlos Alcaraz can't return a powerful forehand down the line.
Djokovic has started this second set impressively.
Image source, Getty ImagesDjokovic 4-6 1-0 Alcaraz*
Novak Djokovic steps into a Carlos Alcaraz second serve to guide a backhand winner down the line, but the Spaniard responds with a laser-like forehand winner.
Djokovic forces deuce with another return winner, this time from his forehand.
Djokovic 4-6 1-0 Alcaraz*
It will be interesting to see how well Novak Djokovic is moving now he is back on serve after seeing the trainer towards the end of that first set.
The Serb seventh seed appears in better spirits with a strong hold to love, sealing the game with an ace down the middle.
Jonathan Jurejko
BBC Sport in Melbourne
He's back. An appreciative roar greets Djokovic when he trudges on to court again.
Nobody on Rod Laver Arena wants to see this one cut short. But how much of a contest will it be?
Djokovic needs all of his super-human powers, it seems.
*Djokovic 4-6 0-0 Alcaraz
Carlos Alcaraz's first serve is on the money as he bring up three set points, before sending down an ace to win it.
Not much Novak Djokovic could do about any of those points.
Image source, Getty ImagesDjokovic 4-5 Alcaraz*
Annabel Croft
Former British number one on BBC Radio 5 Live and BBC Sounds
I've seen Novak Djokovic look injured before, to a point where you feel like he can't possibly run, and he has managed to get through matches and it is quite a miracle.
But he looks like he is hobbling down that corridor. We are so privileged from our position to see every single grimace and facial expression, and it is pretty much happening every time he is hitting the ball...
Image source, Getty ImagesDjokovic 4-5 Alcaraz*
While Novak Djokovic sees the trainer off court, cameras pan to Andy Murray taking a sip from his drink.
I wonder what advice he's given the Serb today about facing Carlos Alcaraz?
A cheer goes around Rod Laver Arena as Djokovic returns to court, with Alcaraz to serve for the first set.
Jonathan Jurejko
BBC Sport in Melbourne
As suspected, Djokovic needs the trainer.
After a quick consultation and a point to his groin, he limps off court for an in-depth assessment in a more private setting.
Djokovic 4-5 Alcaraz*
Novak Djokovic saves a couple of break points but he can't rescue the third as the Serb skews a forehand wide.
Carlos Alcaraz will serve for the first set and the volume levels inside Rod Laver Arena go up a notch.
Djokovic, meanwhile, is taking an off-court break after grimacing during that last game.
Image source, Reuters*Djokovic 4-4 Alcaraz
Annabel Croft
Former British number one on BBC Radio 5 Live and BBC Sounds
It's interesting to see that Djokovic came forward there to keep the point as short as possible.
He doesn't want too many of those long drawn-out rallies.
I think he is hurting. There is something going on with his left thigh I think. He is grimacing and sort of trotting as if there is a bit of a problem there.
Image source, Getty ImagesJonathan Jurejko
BBC Sport in Melbourne
Definitely some discomfort for Djokovic.
Another grimace comes as he staggers to his chair for the towel after another energy-sapping point.
Looks to be limply slightly too, dragging that left leg with him.
*Djokovic 4-4 Alcaraz
Uh oh, Novak Djokovic appears to be moving gingerly now.
Carlos Alcaraz earns break point but the Serb holds his composure from the back of the court to force deuce once more.
Jonathan Jurejko
BBC Sport in Melbourne
Uh oh. This doesn't look good for Djokovic.
As soon as Alcaraz put away that winner for 15-30, he drops to his haunches and grimaces.
A solemn shake of the head goes in the direction of his corner.
Has he suffered a tweak? Or a sense of resignation that this kid is too good?
One to keep a beady eye on.
Image source, Getty Images