The German saves one before he strikes the ball on his... yup you guessed it... forehand side into the netting.

This is truly 'watch through between the fingers'.

Amother double fault. Zverev looks up at his team. They can't help you really.

15-30.

Another double fault.

Double break point.

Painful.

Game.

Maybe after that five-setter against Canadian Denis Shapovalov, he wants an early bath and then get through season two of Cobra Kai.

Carreno Busta mixes up the pace of his groundstrokes - a soft waft is followed by a punishing forehand which shakes the racquet of his opponent at the net.

15-0.

30-0.

David Law
BBC Radio 5 Live Sports Extra tennis commentator

Carreno Busta is making mincemeat of Zverev at the moment.

Zverev comes up short with another forehand. That side is so poor for the German.

Break point.

Taken as PCB hits a brilliant flat winner.

Advantage Zverev. Double fault = deuce.

Hmm...

Leon Smith
GB Davis Cup captain on BBC Radio 5 Live Sports Extra

When his second serve starts to affect him Zverev's forehand tends to go as well. He has got an amazing backhand, he can play those shots beautifully all day long.

Image source, Reuters

The forehand then really lets him down - a wild one aiming for the tramline, but instead finds the depot.

Deuce.

The German then produces a brilliant stun volley at the net, on his forehand side.

Advantage. He needs this.

Oh good grief!

Double fault.

Break point PCB.

Saved.

Relief for Zverev.

Zverev's second serve picks up speed - 133mph. The slower version wasn't doing the trick.

30-15.

PCB then launches a cracking forehand winner down the line. Plenty of top.

Leon Smith
GB Davis Cup captain on BBC Radio 5 Live Sports Extra

That was an unusual first set. Carreno Busta has gone about his tennis in the relentlessly solid way you expect, he's very focused, a good mover and has asked a lot of questions.

He's been solid on first serve and his unforced error count is low, he's just there right at the level.

Zverev's legs look a bit heavy, he came into the net early on trying to be aggressive but that didn't work for him and now he doesn't look like he knows what to do.

He's got to get the balance right to get Carreno Busta off the baseline and try to dictate as much as possible.

Two more errors, the latter - a very weak backhand - earns PCB the first set.

He didn't have to do much to earn the advantage - Zverev's second serve was so weak in that set with only 36% of points won on it.

PCB's forehand goes rogue - his ninth error.

30-30.

You can feel the tension.

Image source, Reuters

Zverev wins the first point before making an error on his backhand and then forehand.

30-15.

He's back in the room.

Zverev shows up to this semi-final and holds with some solid first serves. Four aces now.

Back to you PCB.

Jeff Tarango
Former professional tennis player on BBC Radio 5 Live Sports Extra

I've never seen anyone hit the ball harder than Thiem so I would say he's the favourite. I would like to see Zverev win because the way he plays he would enliven the game for the fans, but he's run into Carreno Busta who always plays so well in New York.

Zverev hits a winner to finally get one break back.

What now?

Justin Timberlake's Rock Your Body rings out around Arthur Ashe. Who will be more inspired by JT? The German? Or the Spaniard?

One saved, then another with a sliced backhand which had dinner for two on the cord before popping over on to the other side.

Luck.