Jeff Tarango
Former American tennis player on BBC Radio 5 Sports Extra

A little bit of nerves there on the Gauff forehand as she is serving for it.

It's been kind of breezy for her, easy for her to go through it, so with a little resistance, is she going to crack?

It's been plain sailing for Coco Gauff so far, until the first moment when it really mattered.

Karolina Muchova draws a couple of errors from the American's forehand to pull one of two breaks back in this set.

Even if she does end up going a set down, that should give her a huge amount of confidence.

Jonathan Jurejko
BBC Sport at Flushing Meadows

A crescendo of applause greets Gauff stepping up to the baseline as she prepares to serve.

The first time the crowd have really got going.

She's serving for the set with only 25 minutes on the board.

That's quicker than the express train back to Manhattan.

Jeff Tarango
Former American tennis player on BBC Radio 5 Sports Extra

Muchova has missed so many sliced backhands but she is still going to the well.

There is nothing really to spark the crowd. A lot of murmurs in the crowd – what is going on.

Maybe she needs to take that sleeve off, and maybe it is too restrictive and is just making her feel uncomfortable.

Coco Gauff looks unstoppable right now.

The American, her every move roared on, breaks Karolina Muchova again, to 15, to set up the chance to serve out the opening set.

Relentless stuff. There only looks like being one outcome in this match right now...

Image source, Getty Images

And there's the first Briton through to a 2023 US Open final.

Andy Lapthorne and his South African team-mate Donald Ramphadi are through to the quad wheelchair doubles final after their opponents retired.

Ramphadi and Lapthorne, who is also through to the semi-finals in the singles event, were 6-2 3-2 up when Slovakia's Tomas Masaryk and Brazil's Ymanitu Silva withdrew.

Jeff Tarango
Former American tennis player on BBC Radio 5 Sports Extra

Maybe Karolina Muchova warmed up early before it got hot and wasn’t able to get back out there again. You warm up in the day, and you feel great but now those strings feel too tight, so you start forcing.

The science of tennis maybe a factor to Muchova’s slow start. A lot of unforced errors so far off both strings for the Czech.

But there's no slowing Coco Gauff down right now.

The 19-year-old races to a love hold to edge closer to the first set. She's given Muchova no hope of a breakthrough so far.

Image source, Getty Images

While the crowd have taken a while to settle down, so has Karolina Muchova.

But the Czech 10th seed is up and running after four games on Arthur Ashe.

A closing ace at 40-30 gets her over the line to ensure she remains just the single break behind.

Image source, Getty Images

There has been a lot of talk around the hot temperatures in New York this week.

That has affected the players again at the US Open on Thursday, leaving doubles player Nicolas Mahut feeling dizzy and Rajeev Ram eating a sushi mid-match.

American Ram asked for the food during his men's doubles semi-final win, later explaining it had been "so hot" that he could not eat enough before the match.

"In the warm-up it felt like I was sweating buckets. It felt like I was depleted a little bit," he said.

It comes after Daniil Medvedev said a player could "die" in the conditions.

The Russian described the heat as "brutal" in his men's singles quarter-final win over Andrey Rublev on Wednesday.

Jonathan Jurejko
BBC Sport at Flushing Meadows

Just the start that Gauff - and virtually the entire stadium - wanted.

Generous applause rings around Ashe, but far from manic euphoria.

Lots of empty seats still.

Plenty will be waiting outside after being delayed making their way out to Queens after work.

Those in the posh seats - including the half-empty Presidential Box - must still be guzzling the champagne.

More spectators filter in at the change of ends, eager to get a piece of the action with Coco Gauff off to a promising start in her bid to reach a first US Open final.

The chair umpire hurries them along, and then has to remind the crowd not to use flash on their cameras, before the players can settle back in.

Jeff Tarango
Former American tennis player on BBC Radio 5 Sports Extra

You can see Karolina Muchova really focused on playing to Coco Gauff’s forehand. [Her coach] Brad Gilbert said he wasn’t going to change the forehand – he was going to show her how to use the one that she has.

Gilbert is just ironing some things out and putting some of the pieces of the puzzle together for her mentally.

Coco Gauff has all the tools, it’s just when do you use this shot or that shot.

Image source, Getty Images

This is a good response by Karolina Muchova, though.

The 10th seed lands a forehand winner on her way to 0-30 on Coco Gauff's serve as she chases an immediate break back.

But Gauff doesn't panic and efficiently swings the game in her favour.

A three-game lead certainly reflects her early dominance here.

Jonathan Jurejko
BBC Sport at Flushing Meadows

To many, Coco Gauff has been a different player since a chastening first-round exit at Wimbledon.

But the key to the teenager's success in the North American hard-court swing has not been making huge technical adjustments.

It has been about restoring faith in the weapons she has, according to Jarmere Jenkins, who is part of her recently-assembled coaching team.

"When you're confident and clear in what you've got to do out there, it puts your mind at ease," Jenkins, who works alongside coach Pere Riba and consultant Brad Gilbert, told BBC Sport.

"Before I feel she was going out there and hoping to play well. Now she is going into a match thinking: 'I've got this if I play well or even if I don't'.

"She doesn't always have to play great to win a match, a lot of matches she has won not playing her best tennis - but the best is going to come."

David Law
Commentator on BBC Radio 5 Sports Extra

Players have started to target the Coco Gauff forehand and I don’t know how that doesn’t get in the head of a player, if she knows people are going to consider it as a weakness, and they are going to pick on it.

She has certainly improved it in weeks and months.

Coco Gauff means business!

Karolina Muchova runs out of answers and is forced into the net, conceding the early break of serve.

Trouble for Muchova.

A sublime backhand lob from Gauff sets up an early break point for the American.

Jeff Tarango
Former American tennis player on BBC Radio 5 Sports Extra

Brad Gilbert has Coco Gauff playing percentage tennis.

She really played great defence in her last match and she’s just showing what a smart player she is.

She is using her speed for defence and then her big shots coming through, instead of letting her opponents get used to her pace.

It's the perfect start for Coco Gauff!

A love hold, sealed with a measured forehand winner after giving Karolina Muchova the run around, settles a tidy opening game to the delight of the home crowd.