Jessica Pegula will face Aryna Sabalenka in the US Open final on Saturday
American Pegula came back from a set and a break down to beat Karolina Muchova
It is a first major singles final for sixth seed Pegula
World number two Sabalenka earlier beat Emma Navarro 6-3 7-6 (7-2)
Two-time Australian Open champion Sabalenka is into New York final for a second year in a row
Listen to live radio commentary from 5 Sports Extra at top of page (UK only)
*Pegula 1-6 0-2 Muchova
It's too easy for Karolina Muchova at the moment.
The US Open crowd are doing their very best to encourage home hope Jessica Pegula.
An overhead lob from Pegula goes long before a volley from Muchova is also wide.
*Pegula 1-6 0-2 Muchova
Jeff Tarango
Former American tennis player on BBC Radio 5 Sports Extra and BBC Sounds
Muchova keeps changing the spins and Pegula likes to meet the straight ball.
Jessica doesn't know what to do right now, she's trying to figure it out.
You can see in her face that she doesn't want to give up.
*Pegula 1-6 0-2 Muchova
Image source, Getty ImagesMore errors from Jessica Pegula whose forehand is long. She then nets as Karolina Muchova goes 30-0 up on her service game.
Another forehand return goes long from Pegula.
There are then two uncharacteristic double faults in a row from Muchova to give Pegula hope.
The sixth seed nets, failing to take the opportunity to get on the board in the second set.
Pegula 1-6 0-1 Muchova*
Annabel Croft
Former British number one on BBC Radio 5 Sports Extra and BBC Sounds
Jessica Pegula seems a bit frozen with fear at the moment.
It's going to quickly turn into a nightmare if she doesn't find some range, rhythm and confidence in her groundstrokes.
Pegula isn't winning her points by winning shots. Usually, when we think of her, she is hitting outright winners and it looks like she just isn't feeling confident at the moment.
We've seen glimpses of what she is capable of but it's Muchova who has been sensational in this match.
Pegula 1-6 0-1 Muchova*
Jessica Pegula was brilliant against Iga Swiatek in her quarter-final match, she needs to find that sort of form again.
The American double faults on her service game and is undone by another sublime Karolina Muchova drop shot.
Pegula responds with a great backhand volley but then fires a forehand wide.
Muchova is a set and a break to the good and Pegula is looking rather despondent.
*Pegula 1-6 Muchova
Annabel Croft
Former British number one on BBC Radio 5 Sports Extra and BBC Sounds
Image source, Getty ImagesJessica Pegula needs to find a rhythm and cut out the unforced errors.
She has been a more aggressive ball striker in the last year but it's not working right now.
Muchova will continue doing what she is doing. She looks at ease and settled in this moment.
*Pegula 1-6 Muchova
Karolina Muchova is moving Jessica Pegula all around the court and forcing errors.
Pegula nets twice as Muchova goes 40-0 up but she manages to win a point with a forehand down the line.
Muchova then responds with an ace to seal the first set with ease.
What a performance from Muchova. Pegula is no match for her at the moment.
Pegula 1-5 Muchova*
Annabel Croft
Former British number one on BBC Radio 5 Sports Extra and BBC Sounds
This is just spectacular what Muchova is doing right now.
Muchova's nerves seem to have settled after coming through that tough game to lead 2-1. It was very stop-start but now she is flowing.
The first few games were so slow and now Muchova is steamrolling her way through. The tennis coming off her racquet is phenomenal.
Pegula 1-5 Muchova*
Karolina Muchova comes to the net and fires a fierce forehand across court with Jessica Pegula moving in the opposite direction.
Muchova is moving around the court with such confidence and she plays another sublime volley past Pegula.
Pegula tries to go for the volley but she nets and Muchova takes her third break point opportunity.
She will now serve for the set.
*Pegula 1-4 Muchova
Image source, Getty ImagesKarolina Muchova races through her service game, going 40-0 up with an ace.
She then swipes a lovely forehand which kisses the line.
The world number 52 is suddenly racing away with the first set.
*Pegula 1-3 Muchova
Karolina Muchova is looking more confident at the moment as Jessica Pegula hits into the net twice.
Pegula won the first point but her game crumbled after that.
Muchova gets her first break at the first opportunity.
Pegula 1-2 Muchova*
Annabel Croft
Former British number one on BBC Radio 5 Sports Extra and BBC Sounds
Muchova is really unpredictable, you never know what you're going to get out of her racquet next.
One moment it's an amazing pick-up shot and then a serve volley but then the next minute it flies off her racquet and she gives away a cheap point.
It's an awkward match at the moment and they will both be able to sense the crowd are a little disengaged with it.
There were some beautiful rallies but it's interspersed al the time with lots of errors and that is very tricky for both of them.
Pegula 1-2 Muchova*
Karolina Muchova's crisp forehand gives her the advantage and then a wild swing from Jessica Pegula means she holds on her service game.
Muchova saved three break points - that could be a missed opportunity for the American.
*Pegula 1-1 Muchova
Jessica Pegula has a second break point opportunity but she is unable to take it and nets.
Karolina Muchova then hits her forehand long to give Pegula break point number three.
Pegula hits into the net as we go back to deuce and you can sense the disappointment.
*Pegula 1-1 Muchova
There are errors from both players in the opening stages.
A well-executed drop shot from Jessica Pegula is followed by a similarly sublime effort from Karolina Muchova to save break point.
Pegula 1-1 Muchova*
Annabel Croft
Former British number one on BBC Radio 5 Sports Extra and BBC Sounds
This match is still a little error-strewn. The crowd haven't had much to get their teeth into.
Everything is being won off errors so far, it's not coming from good shots and that's why the crowd are a little quiet.
Pegula 1-1 Muchova*
Image source, Getty ImagesA few wild swings from Jessica Pegula on her opening service game.
Both players showing early nerves.
Karolina Muchova's forehand then goes long twice and Pegula gets the hold.
*Pegula 0-1 Muchova
Annabel Croft
Former British number one on BBC Radio 5 Sports Extra and BBC Sounds
Jessica Pegula looks a little tentative and a little tight at the moment.
That's what happens when you are nervous. It just feels like you can't release certain things.
It's not a great start for her, a lot of unforced errors.
*Pegula 0-1 Muchova
Karolina Muchova shows some early nerves, catching her toss a few times and netting after winning the first point.
She recovers to go 30-0 ahead and Jessica Pegula's forehand goes long twice as Muchova holds to love.
Pegula v Muchova
Warm ups are complete and we're ready to get under way in the second semi-final at the US Open.
Karolina Muchova will serve first.