And there it is. Aryna Sabalenka sends Anastasia Pavlyuchenkova's serve back into the net.

Unless there's a big momentum shift, Sabalenka's title defence is in big, big danger.

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Anastasia Pavlyuchenkova is on a roll. You can see that confidence as she lifts a deft drop shot just over while Aryna Sabalenka remains rooted to the baseline.

Set point.

Aryna Sabalenka can't quite believe that miss and she stands frozen for a moment with her hands up before trudging back to her chair.

Anastasia Pavlyuchenkova will serve to force a decider.

Aryna Sabalenka drops to her knees in disappointment after miscuing a simple volley and pushing the ball into the net.

It's a completely different reaction on the next point, letting out a scream and clenching her fists. 30-30.

A deft backhand winner gives Anastasia Pavlyuchenkova another break point, though.

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Very, very nice from Aryna Sabalenka.

She slows the point down with a slice to the right before slicing it the other way and watching it swerve perfectly onto the line, leaving Anastasia Pavlyuchenkova with no chance.

Shottt. Aryna Sabalenka takes Anastasia Pavlyuchenkova's serve early and launches her forehand back across the court and into the far corner. Lovely.

Ryan Harrison
Former American tennis player on BBC Radio 5 Live and BBC Sounds

Pavlyuchenkova has just absolutely turned it on.

It hasn't necessarily been Sabalenka making a whole lot of mistakes, it has been more about the story of Pavlyuchenkova just being completely in control.

It seems like every ball she is striking is near the baseline, if not on the baseline, and all Sabalenka can do is stand there star-struck.

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That's better from Aryna Sabalenka. She switches up her game plan, attacking the serve before dashing to the net and lifting a volley just over.

Now it's Anastasia Pavlyuchenkova's turn to let out a yell of frustration as she loops a forehand wide before going long and taking us to deuce.

Aryna Sabalenka shrugs her shoulders after saving the first break point with a huge forehand winner.

But she can't save the second, and she lets her frustrations show as Anastasia Pavlyuchenkova gets the double break.

Ryan Harrison
Former American tennis player on BBC Radio 5 Live and BBC Sounds

You can see that Sabalenka is starting to feel the pressure mounting.

Pavlyuchenkova was in firm control at 40-0 in the third game of this second set - and it has been absolutely one-way traffic since then.

Where has this come from? Aryna Sabalenka was ruthless in those longer rallies during the first set, but it's Anastasia Pavlyuchenkova who is putting them away now.

She's winning the battle of the big hitters at the moment and she's got herself another two break points.

That Anastasia Pavlyuchenkova break makes this match a whole lot more interesting. How will Aryna Sabalenka respond?

The second seed seems a little rattled as Pavlyuchenkova confidently wraps up a hold to 15.

SHE CAN!

Anastasia Pavlyuchenkova wins her fifth point in a row, fighting back from 0-40 down, with a stunning forehand winner straight down the line.

Aryna Sabalenka had no chance.

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Here we go then. Aryna Sabalenka finds the fence.

Can Anastasia Pavlyuchenkova make the most of this break point?

She thought about it! Anastasia Pavlyuchenkova almost crashes her racquet off the ground, but she rethinks the decision and only lets it drop from a couple of inches.

The Russian will need to do better than that on Aryna Sabalenka's serve if she's to have any chance of reaching the semi-finals.

And she does! Clawing a few points back to bring up deuce.

Ryan Harrison
Former American tennis player on BBC Radio 5 Live and BBC Sounds

This is electric stuff from Aryna Sabalenka.

One thing I love about her is how quickly she starts second sets after securing the first set. We sometimes see players having a bit of a let-down after taking the first set, thinking that they are already one set to the good.

But Sabalenka immediately puts you under the gun - and that is why she is so dominant.

Jonathan Jurejko
BBC Sport in Melbourne

Image source, BBC Sport

Novak Djokovic was warming up on Rod Laver Arena earlier to prepare for tonight's blockbuster with Carlos Alcaraz.

And he had the help of a Brit. Well, two actually.

British number three Jacob Fearnley played the role of Carlos Alcaraz as he hit with the 24-time major champion - as Djokovic's coach Andy Murray kept his beady eye on things.

Detailed attention was paid by Djokovic - who was directing Fearnley about what he wanted - on his first returns out wide on both ad and deuce side.

Once they had wrapped up, the hundreds of early-birds were waiting for the night session got another treat.

Murray jogged on to court, greeted by shrieks and cheers, and knocked a few gentle balls to his once great rival. He even made a dash to the net when Djokovic cheekily pulled out a drop-shot.

Don't worry, he was smiling rather than grimacing.

Image source, BBC Sport

Anastasia Pavlyuchenkova wriggles free as Aryna Sabalenka overhits her backhand return.

The 27th seed needs to stick with Sabalenka in this second set. So far, so good.

Ryan Harrison
Former American tennis player on BBC Radio 5 Live and BBC Sounds

If Pavlyuchenkova is up in her service game, even at 30-30, she has got to make sure that she gets the ball out of the middle of the court. She needs to get it back short in the court towards Sabalenka's forehand.

All of these points, where she is erasing those deficits, are coming with just a quick one-two punch. She has got to get a little more depth on the return.

A flurry of backhand attacks from Aryna Sabalenka pull her up to 15-15 before Anastasia Pavlyuchenkova wrongfoots the second seed with a clever cross-court backhand.

Oh! Now that would have been a cracking shot if Sabalenka had made it. She slides halfway across the court to sweep a forehand back in around the net post, but it goes long.

Again, the second serve is fair game for Sabalenka and we go to deuce.