A big few points in Petra Kvitova's US Open. She had the momentum before the roof closure, now she's trying to hold off a rejuvenated Venus Williams.

Break point for the American.

Williams screams a forehand on the stretch back into Kvitova's path, the Czech bends her knees, lines it up and... catches the net.

She dusts herself off with a mammoth serve that skipped up towards the head of Williams, who somehow manages to wriggle it beyond the tape and we have 30-30.

That's just the service game Venus was after following that short closing-the-roof delay, but it's Kvitova who takes the prize for best challenge so far.

That looked in to me, and to the umpire, but Hawk Eye says no.

It's just a minor disturbance for Williams, mind. She holds.

Piers Newbery
BBC Sport at Flushing Meadows

The sound of paper cups flying out of hands and a rapidly emptying South Plaza suggests the locals are wiser than me, by both clearing out and packing waterproofs.

Image source, BBC Sport

Enough rambling. Time for tennis.

We left you with Venus Williams about to serve.

Petra Kvitova jogs to her end, does a couple of squat jumps and then waits for the American to fling one in her direction.

Rose Richards: Heart says Venus in two. Head says Petra in three.

David Law
Radio 5 live sports extra commentator at Flushing Meadows

I don't think that there is going to be much of a dry up on the court now. They got the roof across pretty quickly. A couple of ball kids with white towels are out, drying off the lines.

Image source, Getty Images

How would you describe Venus Williams' choice of outfit? I reckon it's got a bit of 'Wilma Flintstone does tennis' about it...

We have roof news... it's closing. Because there's 'weather in the area'.

Both players are back in their seats, towels draped over their shoulders in a bid to keep warm.

It shouldn't take long. It's almost closed... I promise.

Image source, Sloane Stephens

This is what two hours and 28 minutes of tennis, culminating in a final-set tie-break, does to you.

Sloane Stephens awaits the winner of Kvitova-Williams in the semi-final.

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David Law
Radio 5 live sports extra commentator at Flushing Meadows

If Petra Kvitrova could bottle this backhand and replicate it whenever she wanted, she would be the best player in the world.

Kvitova shows she can also mix up her service game and sends Venus sprawling towards the tramlines.

The Czech has Williams on the run again, sucking her into the net with the deftest of drop shots and then nonchalantly volleying a winner down the middle.

A fabulous cross-court backhand puts Kvitova in the driving seat once more and, finally, the 27-year-old sees off the threat of Williams.

Image source, Getty Images

David Law
Radio 5 live sports extra commentator at Flushing Meadows

It is a really strange sight to see the Petra Kvitova backhand being solid as a rock and the forehand flailing around.

Image source, AFP

Image source, Getty Images

If the first set was thunderous, full of unforced errors and a bruising battle of big serves, then this second has slowed its way into some engaging rallies.

There's a buzz around Ashe, but it's one of slight concern - that and probably wondering what's for dinner - as Kvitova looks to take the game to Williams.

But it's the consistency of the American that's winning out. Two break points.

Piers Newbery
BBC Sport at Flushing Meadows

"Who is that?"

"Boris Becker."

"Boris...... Becker...."

I can't be sure that everyone gathered to watch Boris Becker carry out TV duties was totally familar with the 1989 US Open champion, but plenty were as he drew a crowd outside Ashe. Media work must now be combined with his new role as head of German tennis, so a busy time ahead.

Image source, BBC Sport

Image source, Getty Images

Venus Williams takes inspiration from a Test match bowler and throws in a slower serve that catches out Kvitova.

We go to deuce, and Kvitova appears to be finding her range. What's left in the Venus bag of tricks?

Not that slow second serve. Kvitova gobbles it up and then muscles in on a net ball to power her way into a break.

The first-set stats don't make pretty reading for Petra Kvitova - only 3/10 points won on second serve. 13/23 on first serve isn't too clever either.

The winners-unforced errors count was 8-8 for Williams and 6-16 for Kvitova.

Going for too much?

Image source, Getty Images

It's a good recovery from the Czech. When she gets her eye in, there aren't many players on the circuit who can out-power her.

Kvitova punches her way to 40-15 and then leaps up to meet a bouncing Williams return with a two-handed backhand that skips beyond the American before she even has chance to swivel in its direction.

Image source, Getty Images

That's the first set Petra Kvitova has lost this tournament.

She starts the second in the same way she began the first, with a double fault.

Jeff Tarango
Former professional tennis player on 5 live sports extra at Flushing Meadows

That was a pretty impressive set from Venus Williams, coming back from 3-1 down. There were 16 unforced errors from Kvitova after she started off on top.

I would tell Kvitova to go for one big serve per game and for the rest, keep mixing up the variety. She needs to throw in a few more slice shots with her groundstrokes as well.