Oooof. We've not seen much of that, a delightful, dipping slice from Kvitova that leaves Williams with no room to pick it up off the surface.

She's using her entire arsenal of shots out there to stop the American breaking back.

Kvitova thinks she's added an ace to the pile. She's walking, but it's let.

That's ruthless from the 13th seed, serves, slices, volleys.. and she takes six points on the trot to hold.

Image source, Getty Images

Kvitova takes the opportunity in her time between end changes to apply some cream to her hands - she says it has helped her comeback after the knife attack nine months ago.

Williams takes the game to the Czech, though, and quickly earns three break point chances.

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

This is a real match based around how long you have been playing the game, what you have learned in the past and how much you want to be part of the big days in the future.

There is no meter on those factors for these two.

Someone's got the binoculars out. They'll need more than that to catch a glimpse of some of these power strokes - like a fleck of green skimming across the deep blue Ashe court.

Petra Kvitova shows all of her punch at the net to force a volley on the stretch beyond Williams and level at 30-30, and then fizzes a forehand return with similar ferocity to earn a break point.

She takes it!

Image source, AFP

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

Petra Kvitova has expended a lot of energy with those c'mons and hauling her way back into the match.

There is nothing to choose between the two really, but if you pushed me I would say that it is a 51%-49% call in favour of Venus Williams.

That ferocious first serve from Kvitova didn't seem to jump up like Williams was expecting it to, and another powerful stroke from the 27-year-old quickly turns the game in her favour.

It's wild from Williams as Kvitova delivers another unreturnable serve and the Czech holds.

It's Kvitova on serve, but Williams directing the points. Knee bent so low it's almost scraping the Ashe floor, she guides a backhand beyond her Czech counterpart - 15-30.

It's going to be a severely restricted programme at Flushing Meadows on day 10 because of a very poor weather forecast.

The two men's quarter-finals and two women's quarter-finals will take place as planned on Arthur Ashe Stadium, which, of course, has a roof (that is currently in use).

Three women's doubles matches remain on the schedule on Grandstand court but that's it.

Image source, BBC Weather

For the second women's quarter-final in a row, to a third set we go.

Venus Williams gets the final set going, but I imagine she'd probably like this crowd to settle down somewhat. It's like collecting time at mums and toddlers.

You can sort your play dates once the tennis has finished.

Williams races into a 40-0 lead, and eventually snaffles up the point she needs to hold.

Image source, Getty Images

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

Right now, Petra Kvitova has the momentum and the energy to take the third set, but don't bet against Venus Williams' wiles and experience.

I think the key will be the second serves, Petra Kvitova was able to pick off easy points off Venus Williams's second-serve tee-off in the first set.

Kvitova has just lost a bit of sharpness towards the end of this second set - can she close it out?

Williams welcomes a mistimed stroke that goes long, but the Czech shows she can compete at the net as she forces the American wide before galloping forward to level things up.

Image source, Getty Images

Petra Kvitova looks to slice a backhand towards the baseline but misjudges her length and Venus Williams holds.

Image source, Getty Images

New balls. And renewed vigour from Venus on her serve as she correctly challenges a Kvitova return that goes long.

An ace that fizzes off the blue surface takes Williams to 40-0, but a foot fault gives the Czech a sniff.

And Kvitova pins Williams on the baseline to make it deuce.

David Law
Radio 5 live sports extra commentator at Flushing Meadows

Venus Williams had won seven out of eight points, but Petra Kvitova put the plug in her momentum with some immaculate serving and one massive forehand.

Petra Kvitova's winning howl echoes around the stadium now the roof has closed. These New Yorkers are in no doubt as to which player just clambered her way out of a break point-shaped hole.

What a hold.

Image source, Reuters

Somehow, Venus Williams is getting a limb to every Kvitova forehand.

It's bringing me out in a nervous sweat at memories of the Bleep Test in PE as she does shuttles across the Arthur Ashe court, but it's working.

Some 37 years old and with the endurance of an elite marathon runner, Williams squeezes her way to two break point opportunities.

Image source, Reuters

Scintillating from Williams. She glides way out beyond the right edges of the court to skittle a forehand winner back the way it came.

No messing from the two-time US Open champ. In, out, holds serve.

Kvitova has found her range with her first serve in this set so far - winning 12/13 points (92%).

She's 4/12 on second serve in set two (33%).

Winners-unforced errors count?

Williams 1-2

Kvitova 13-9.

It's on her racquet at the moment.

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

That is a big hold from Petra Kvitova. But I think that the Czech's celebrations - she roared a couple of c'mons - have riled Venus Williams a little bit. There was a little bit of a look at the changeover.

Kvitova throws her whole body into a serve that Williams can only dangle a frame at, it drops into mid court and the two-time Wimbledon champion follows up with just as much force and fury.

She holds. And lets out a roar of approval.

Image source, Reuters