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Umpire Keothavong gets out of his chair to call Jakub Mensik's serve in - an ace. Alexander Zverev isn't amused. 30-15.

However, from 40-15, Mensik is pulled back to deuce with a couple of tired shots.

Alexander Zverev offers up a resigned flap of the arms as umpire James Keothavong penalises him for a time violation after the change of ends.

Mark Woodforde
17-time Grand Slam doubles champion on BBC Radio 5 Sports Extra 2 and BBC Sounds

I guess it has been a bright positive response from Alexander Zverev after losing that first point in such a fashion.

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Jakub Mensik takes a 0-15 lead - the ball spooned up off his racquet and clipped the net chord on its way down, completely bamboozling Alexander Zverev. Both players stare in disbelief.

However, Zverev doesn't let it faze him, racing through the next four points to hold. He's two games away from a fourth Grand Slam final.

Naomi Broady
Former British player on BBC Radio 5 Sports Extra 2

It was a must-win game for Jakub Mensik.

It is suddenly becoming a battle again for the first big strike.

A huge hold and a must-hold service game.

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This time the drop shot comes good and Jakub Mensik is on the board in the fourth set! Two break points saved, four deuces navigated.

Jakub Mensik keeps himself alive! A big serve gives him an early foothold and he stretches Alexander Zverev off the court with an equally large forehand.

Another short shot doesn't come off. Ominous times.

Jakub Mensik wastes advantage again. His drop shot is overcooked and Alexander Zverev pounces with a forehand down the line.

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Alexander Zverev has started to target Jakub Mensik's backhand. He steps inside the baseline to pound one down the line and Mensik can't get it back into the court.

Jakub Mensik, coming into the net, gets down low to pick up a backhand and Alexander Zverev, sliding forward, can't reply.

Break point saved.

Mark Woodforde
17-time Grand Slam doubles champion on BBC Radio 5 Sports Extra 2 and BBC Sounds

There is the response that we have not seen in the past in these situations from Alexander Zverev. It is turning for him.

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Jakub Mensik has deflated like a balloon in this fourth set, looking pained and rueful as Alexander Zverev's cross-court return floats just over the net and in. 15-30.

Zverev sends a loose forehand into the net but manipulates Mensik back and forth across the baseline to force a backhand error and earn a break point.

Mark Woodforde
17-time Grand Slam doubles champion on BBC Radio 5 Sports Extra 2 and BBC Sounds

I am really encouraged to see Alexander Zverev play.

He is willing to risk moving forward, and it puts the onus on Jakub Mensik to come up with something grand.

The scoreboard pressure is singing loudly.

Naomi Broady
Former British player on BBC Radio 5 Sports Extra 2

Alexander Zverev is a man on a mission. I think he wants this so much, and he has obviously had that conversation that nothing is going to distract him out there.

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Alexander Zverev plants back-to-back groundstrokes, one off either wing, into the net to trail 15-30.

He recovers to lead 40-30 - including a fine body serve which Jakub Mensik can only return long - and thinks he's clinched the game with a shot from Mensik drifting into the tramlines.

He's called back by umpire James Keothavong as he heads to his chair - "it's good, Alex" - but wins the replayed point.

Naomi Broady
Former British player on BBC Radio 5 Sports Extra 2

Sustaining your intensity and holding your level of focus, but the smallest blink can make such a difference. What a cushion Alexander Zverev has now.

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That's a poor shot from Jakub Mensik, who puts his hand to his mouth after sending a routine backhand a couple of feet long. Alexander Zverev mis-hit his return but the bounce for Mensik wasn't especially unkind.

Jakub Mensik plants a tired backhand in the net.

Alexander Zverev has been clinical with his break point opportunities in this match - can he strike early in the fourth?

A couple of unforced errors at 30-15 and 40-30 from Jakub Mensik... we're going to deuce.