Danny Morgan:, external Devastating end but Wozniacki is on a mission. She beats Serena in an epic 3 setter tomorrow.

Image source, Getty Images

You hope it's only a temporary problem for Peng, rather than something more long-term. It looked like her body began to cramp, first in her legs, then her shoulders. It's quite distressing to see an athlete taken away in a wheelchair.

Caroline Wozniacki: "It was very difficult to watch. You want to battle and finish it properly. I feel sorry for Peng because she played really well. I hope she'll be OK.

"I feel pretty good. I've been in bed for the past two days, but I feel good now. The crowd was amazing, cheering me through.

"It's incredible to be in the final, I have goosebumps. I'll go to have an ice bath, then watch the other semi."

A sad, but inevitable end. Caroline Wozniacki has won this match and is through to the US Open final, but concern is for Peng Shuai, who looks to be going in to a full-body cramp. She is helped into a wheelchair and taken from the court, applauded by the crowd and Wozniacki.

Jeff Tarango
Former professional tennis player on BBC Radio 5 live sports extra

"Wozniacki is feeling this. It's like the boxer who doesn't want to hit the guy because he's done."

Image source, Reuters

That serving practice has done Wozniacki some good, the ball landing to save the break point. Hang on, what's going on here? Return winner from Peng, then, unbelievably, another double from Wozniacki gives Peng one more break point. Barely able to move, Peng goes long and goes to her knees once more, with an unreturned serve leaving Peng on all fours on the ground. Now, Wozniacki is checking on her stricken opponent.

We've gone 10 minutes since the last point. The medical timeout is over. Here comes Peng Shuai. She looks emotional, but, remember, she's got a break point...

Piers Newbery
BBC Sport at Flushing Meadows

"Peng leaves for medical "evaluation" before it's announced as an official medical timeout. "If she evaluates for half an hour, everyone could be ready again," says Wozniacki. Confusion on and around Arthur Ashe Stadium."

Jeff Tarango
Former professional tennis player on BBC Radio 5 live sports extra

Image source, Reuters

"I don't think Peng will be able to continue. They are taking precautions and giving her the chance, but I think it was so severe I think she will say she can't walk back on to court."

Wozniacki looks to be getting a little antsy, questioning the chair umpire. She goes back to the serves - if she's not careful, she'll need treatment on her shoulder. Now it's time for a sit down and a drink, then wait. Peng is out of sight, while music plays over the tannoy.

In case you were wondering, Wozniacki is still netting those serves. The umpire tells us that Peng is being evaluated by the doctor. The busiest people on court are the ball-boys, as three of them have to relay balls back to Wozniacki.

Still Wozniacki practises as Peng is helped to her chair. Is this the end of the match? What a sad end if it is. The ball-boy brings an umbrella to shelter Peng while Wozniacki asks what is going on. There's people all over the court while the Dane continues to serve to no one. Strange scenes.

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Is that right, is Wozniacki crying? The referee is out there. Peng is at the back of the court, leaning on the boards. What was thought to be cramp looks like a right knee problem. Now it's the Chinese in tears as Wozniacki practises her serve. Bizarre drama.

Jeff Tarango
Former professional tennis player on BBC Radio 5 live sports extra

"Wozniacki is crying because it's disturbing her so much. She just rubbed her eye. It's emotional. About 99% of cramp occurs because of nerves and because a player wants this so much."

Wozniacki has the wind behind her as shadows gradually begin to creep across the court, but she shows her frustration in the shape of a right foot aimed at the ball as yet another double fault gives Peng a 15-30 lead. "Come on," says Wozniacki as she gets back on terms, with Peng then hopping around because of cramp in her right thigh. The crowd applaud encouragement. Just land the serve, right, Caroline? You can't believe this. Double fault. Peng still hobbling, barely able to stand. Here comes the physio...

Jeff Tarango
Former professional tennis player on BBC Radio 5 live sports extra

Image source, AP

"Wozniacki is thinking it doesn't matter if she's serving or returning, it's eight points to win and reach the final. She only needs to think about that."

Peng isn't going quietly, though, reminding Wozniacki that there's still work to do with a big double-hander that has the Dane floundering. Ah, this won't do. Two backhands landing wide, 40-40. Under pressure, Peng responds, battering home a smash, then serving an unreturnable. No gimmes for Wozniacki.

The rapid fire of camera shutters click as Wozniacki tosses the ball into the blue New York sky. Peng's forehand not coping well, though a seventh double fault from the Dane brings us back to 40-30. Once more, though, the Peng forehand can't do the business, and a dump into the net puts Wozniacki one step closer.

Image source, Getty Images

Is that the ball game? Wozniacki gobbles up the Peng serve for her third game in a row and a break advantage. The 10th seed hasn't been a great leader, but she's now only three games from the final. She removes her ice towel and heads back on to court. She may only feel its cool fluffiness once more.

Peng is showing the odd sign of cracking, leaning on her knees as a forehand goes wide. More frustration, giving another forehand too much welly. 0-30. Hmmmm. Is it falling apart? Double fault. Three break points.