A huge serve takes Jannik Sinner one point away from the second set.

Two set points.

Alexander Zverev is fuming. All Jannik Sinner can do is hold up his hands in apology as the ball clips the net cord and trickles over to Zverev's side of the net. 5-4.

Not much Alexander Zverev can do about that serve, but Jannik Sinner flings a forehand wide. That's a poor miss, that. 4-4.

Jonathan Jurejko
BBC Sport in Melbourne

Cor blimey! That epic 21-shot point in the 12th game got folk out of their seats.

Sinner stares ice-cold straight at his team before flashing a quick glance at his opponent.

Zverev has the look of a man whose carrier bag has just broken on the way home from the supermarket.

Frustration, surprise and perhaps anger he didn't go for greater insurance.

Back and forth we go. Jannik Sinner pulls us level with a mishit forehand that flies high and wide.

Annabel Croft
Former British number one on BBC Radio 5 Live and BBC Sounds

Zverev is playing much better points now.

He looks more confident and more at ease. He looks to have less stress in his body when he strikes the ball.

I feel like his level has been fluctuating and clunky all the way through this match, but he has done a great job to keep it where it is at.

I feel like he can only go in one direction - and that's better - but he might run out of time before he does...

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Alexander Zverev can't quite believe he's missed that and he waits for the replay to show him that it's actually long by a couple of inches.

And there's another poor miss from the second seed. 3-2.

Jannik Sinner comes to the net to swipe home a volley, but the defending champion goes long on the next point and gifts Alexander Zverev with a mini-break. 1-2.

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Alexander Zverev is first to serve in the tie-break and he gets the opening point with big forehand striking that eventually takes it's toll on Jannik Sinner. 1-0.

Ah. The drop shot from Jannik Sinner doesn't have enough pace to pull it over the net.

WOW. Sinner, for some reason, goes for the same drop shot again. It gets over the net this time but Alexander Zverev gets there and takes charge of the point, sending the Italian one way then the other.

Yet it's Sinner who comes out on top with a brilliant pass down the line. A fantastic point.

We go to a tie-break.

Annabel Croft
Former British number one on BBC Radio 5 Live and BBC Sounds

This is going to feel so much better for Alexander Zverev because he isn't having to fight his way through service games.

Alexander Zverev delays Jannik Sinner's serve by complaining about the position of the spider-camera overhead.

It seems to only have helped Sinner, whose kick serve catches out the German.

But there's a rare double fault from the defending champion. 30-15.

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Jannik Sinner miscues his strike, skewing the ball up and out before an ace brings up game point for Alexander Zverev.

And after a miss, there's a fiery forehand to get the job done.

Back to you, Jannik.

Jonathan Jurejko
BBC Sport in Melbourne

Sinner falling 0-30 down for the first time in the match gets Melbourne murmuring.

Then he locks in on his first serve.

Mixing it up by going down the middle and out wide keeps Zverev guessing - and firmly shuts the door.

On we go. Jannik Sinner wins four points in a row to claw his way back and hold serve.

Pat Cash
Former Wimbledon champion on BBC Radio 5 Live and BBC Sounds

Alexander Zverev is doing his best, isn't he?

He is really trying to get back into this match. He is putting together some good rallies, just dropping some shots short and mixing it up.

But Jannik Sinner is just ripping into these forehands - boy can he get some pace off them!

Or not. Jannik Sinner gets back on track with a drive volley winner before Alexander Zverev finds the fence. 30-30.

Two big misses from Jannik Sinner, and all of a sudden Alexander Zverev is in with a shout here. 0-30.

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Alexander Zverev hangs on.

A solid hold for the German and he piles the pressure back on Jannik Sinner, who has to keep serve to stay in the set.

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