From 60%, down to 50%, a third break point gone. In Peng's defence, it's a brutal Wozniacki forehand that saves it, with Peng then going long with a forehand of her own. An important Wozniacki hold is completed when Peng goes into the net, getting us back on serve in the second.

If Peng goes on to lose this, she might reflect on missed opportunities. Wozniacki has taken all three of her break opportunities, while Peng has taken only three of five. 60% is decent, but not good enough when your opponent is up at 100%. Wozniacki, though, is presenting another chance to the Chinese. Double fault. Break point number two.

Image source, AP

Those drunken singers have got Sweet Caroline stuck in my head. For what seems like the umpteenth time in the match, the ball is given some huge hang time in a marathon rally, Peng eventually going wide with a forehand. The Dane follows up with an ace, but is totally stunned by a a Peng reaction volley. That ball was rifled at the Chinese, but the doubles specialist somehow got it back. Wozniacki can't get there and gives away another break point with a wild forehand.

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

"Don't start thinking about the ramifications of winning this match because that's when you go into a tailspin. It goes against human nature but you have to do it."

Peng has just never looked comfortable in the lead, while Wozniacki comes to the fore when she's forced to chase. A forehand in the fish-catcher means Peng surrenders the break she earned in the previous game. Back on serve in the second.

All happening. Wozniacki looks to take Peng's head off, only for a stabbed volley to limp over the net. Ultimately, though, Peng's scampering isn't enough to prevent 30-30 and a double fault give Wozniacki the chance to break back...

Image source, Gael Monfils

Gael Monfils, who lost to Roger Federer in five sets on Thursday, on Twitter:, external I will keep working harder to maybe have one day my picture next to my idol. A big thx to all my fans.

So often in this match, Wozniacki has been at her best with her back pressed against the Big Apple. She's scrapping here, only for the forehand to break down once more. Wild and wide, Peng tacking an early break in the second.

Jeff Tarango's view is probably a popular one - you'd suspect Wozniacki could pull away. No one seems to have told Peng Shuai, though. Twice she forces Wozniacki errors for 15-30. Jolted into life, Wozniacki urges her long legs to the net to pass, only to be left static when Peng blast a backhand past for a break point...

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

"Wozniacki will be looking to roll through this second set. I don't see any way Peng can raise her game to stop her now."

Image source, EPA

Peng, jet black hair in a neat ponytail, is booming down the serves to little fanfare. Two not returned, with her first ace sandwiched in between. The crowd are non-plussed, though, barely any applause to appreciate her efforts. Is that someone singing Sweet Caroline? Come on, we can do better than that.

Piers Newbery
BBC Sport at Flushing Meadows

"There's not much doubt who the crowd are favouring, with plenty of "C'mon Caroline!" to be heard as this enormodrome slowly fills up - best guess is about two thirds or 15,000 in now, which is about what Centre Court holds.

"Peng had won 40 service games in a row before Wozniacki broke through in that set, and the Dane edged it despite struggling with the wind."

Shots of the outside courts show Roger Federer chatting with Kei Nishikori. "Listen Kei, this is how you beat Novak." The players are back, Wozniacki complete with ice towel. She rises from her seat first and will be on the receiving end of the Peng serve.

David Law
BBC Radio 5 live sports extra commentator

"Wozniacki's defence has been magnificent. She has dealt with everything Peng has thrown at her and it looked for the first time during that tie-break as if the effort was getting too much for Peng."

One is all she needs. From Peng Shaui serving for the first set, Caroline Wozniacki has turned it around to race through the tie-break. Peng is a set down for the first time in the tournament, while Wozniacki is one step closer to the final. Both head off court at the end of a very watchable opening chapter.

Yep, it's turning into a procession. Woznicaki changes ends at 5-1, then, playing with great freedom, earns five set points.

Image source, Reuters

Peng is creaking here, looking quizzically at her racquet as if it is the strings that are letting her down. Wozniacki, all flowing forehands and slicey backhands, has been at her best since Peng served for the set. The Dane leads 4-1.

Peng immediately earns a mini-break thanks to a Danish error, then is engaged in an age-long battle of attrition. Back and forth, ball sent skywards, coming down with snow on. Wozniacki puts away the smash, then forces Peng to net. No points won on serve yet in this breaker.

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

"Wozniacki doesn't quit. She's a great fighter, even when she was not playing well or as fit as she has been, she was still a great fighter."

We're going all the way. Peng's backhand completely lets her down, meaning we need the shootout. No time to draw breath.