Another brilliant shot into the empty space brings up 0-30 for Sabalenka on the Pegula serve before she brings up a couple of break points with some aggressive groundstrokes.

Sabalenka produces some big shots to take a very comfortable and rapid hold to love.

Still on serve in set one.

Image source, Getty Images

With Jessica Pegula and Amanda Anisimova both featuring in the last four in New York, it marks a third consecutive year that the American crowd have two home players in the semi-finals.

Plenty for them to get behind.

Annabel Croft
Former British number one on BBC Radio 5 Sports Extra and BBC Sounds

It's feeling pretty neck and neck at the moment. Already the crowd is quite engaged.

Ouch. Pegula begins her second service game with a double fault. That's two already in this match.

She hangs in there to win the next couple of points before Sabalenka winds up the backhand but can only slam it into the net.

Another hold for the American.

Image source, Getty Images

David Law
Commentator on BBC Radio 5 Sports Extra

We have seen more than once a crowd get behind an opponent and bother Sabalenka. Against Coco Gauff here a couple years ago, and again at the French Open this year. She couldn't handle this at the French Open.

Jonathan Jurejko
BBC Sport senior tennis reporter at Flushing Meadows

When Sabalenka cannot find a way in the biggest moments, she admits it is because she is known to "lose control", mentally and emotionally.

In Melbourne, it was frustration at being unable to cope with Madison Keys' destructive power.

At Roland Garros, it was fury at hitting 70 unforced errors as Coco Gauff fought back.

At Wimbledon, it was fear at not matching Amanda Anisimova's bravery.

"I think it's good she is emotional. But it's about having control over those ups and downs," Max Mirnyi, who she recently added to her coaching team, told BBC Sport.

In New York tonight, so far, we have seen a couple of the usual heaving sighs and curled lips - but not many as she continues to hold serve.

We all know that one of Sabalenka's big strengths is her power. But sometimes she can be a little over zealous and that results in errors.

Today she'll have to control all of that.

A ridiculously good cross-court forehand that kisses the line wraps up another hold for the Belarusian.

Annabel Croft
Former British number one on BBC Radio 5 Sports Extra and BBC Sounds

Such a relief for Pegula to get on the scoreboard and settle the nerves. A good start from her on her service game.

Image source, Getty Images

Big support for Pegula as she steps up to the baseline to serve then even more noise when she wins her first point on serve.

That's followed by a double fault, though, which is not greeted with the same enthusiasm but a few big serves get the American on the board in this semi-final.

Annabel Croft
Former British number one on BBC Radio 5 Sports Extra and BBC Sounds

We know how well Pegula has been allowed to play this tournament. But maybe Sabalenka isn't going to allow her to play her best tennis.

Image source, Getty Images

Sabalenka on the board with a comfortable opening service game.

One overcooked forehand means it's a hold to 15 and not to love but it was pretty swift all the same.

Off we go then. A place in the US Open final awaits the winner.

Sabalenka to serve first.

* denotes server

One thing Aryna Sabalenka has on her side is that she's had an extra couple of days off.

Sabalenka has not played since Sunday, after injured quarter-final opponent Marketa Vondrousova withdrew less than two hours before Tuesday's match.

Can a walkover be a blessing and provide a recharge? Or a curse because it ruins rhythm?

"It can be tricky," former Wimbledon champion Marion Bartoli said on Sky Sports.

"That's why every single person in her team has to play that role of making sure the body is functioning properly and making sure her mind is there."

In a bid to avoid any ring-rust, Sabalenka and her team have been hitting the practice courts hard.

After discovering Vondrousova's misfortune, they spent about an hour practising on Tuesday evening to simulate a match scenario.

"I just wanted to move and throw the energy I had," said Sabalenka.

"I wanted to sweat and pretend it was an activity, or a match or something."

Image source, Getty Images

Aryna Sabalenka leads the head-to-head stats with seven wins to Jessica Pegula's two.

The last three of those have come in big finals - at the US and Cincinnati Opens last year and in Miami earlier this season.

Eight of those nine meetings have been settled in straight sets.

Image source, Getty Images

Joe Salisbury and Neal Skupski have reached the men's doubles final on what has been a largely positive day for British players at the US Open.

The sixth seeds beat Yuki Bhambri and Michael Venus in a deciding set on Louis Armstrong Stadium.

In the men's wheelchair singles, Alfie Hewett beat Tom Egberink of the Netherlands in straight sets to reach the semi-finals, but Gordon Reid was defeated by Spanish third seed Martin de la Puente.

Later in the day, top seeds Hewett and Reid got through to the final of the doubles event.

Andy Lapthorne is through to the last four of the quad singles after a three-set win over Australia's Jin Woodman, but compatriot Greg Slade lost to top seed Niels Vink.

There's also still the possibility of an all-British final in the girls' singles, as second seed Hannah Klugman and defending champion Mika Stojsavljevic made it through to the semi-finals with straight-set victories on Thursday.

As the players begin their warm up, let's take a look at what else has been going on today...

Annabel Croft
Former British number one on BBC Radio 5 Sports Extra and BBC Sounds

It's an exciting semi-final. I'm glad they've closed the roof, it was awful conditions and I feared for the players. I think we will get better tennis now.

Here come the players out onto Arthur Ashe.

Neither Aryna Sabalenka or Jessica Pegula have dropped a set so far at the New York major.

That will of course have to change tonight.

Jessica Pegula reaching the final of last year's US Open was her maiden appearance in a major final.

Prior to that she had never gone past the quarter-final phase of a Grand Slam.

And since that run to last year's final in New York she has had disappointing campaigns at the other three majors this year, suffering early exits in Australia, France and Wimbledon.

But there seems to be something about this tournament for the fourth seed.

Image source, Getty Images