Great reactions from Karolina Muchova as Jessica Pegula's forehand skips up off the net cord and the Czech readjusts to slam it into the corner. 30-30.

A 16-shot rally ends with Pegula stretching into the corner and hooking into the net.

Break point for Muchova.

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

Jessica Pegula is back to striking with authority from corner to corner and moving up the court when she sees the damage that that ball has done and she knows she can take time away by moving forward.

Jessica Pegula just can't put a foot wrong as she wins a fourth game in a row and earns an early break in the final set.

Pegula has won eight of the last 10 games.

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

I think we're in for a tussle, I think it is going to be a fanatsic final set.

But disappointing from Karolina Muchova, the way she just evaporated. All those unforced errors.

I didn't expect Jessica Pegula to get back into it in the way she did, that was a pretty big turnaround.

A strong start to the final set from Jessica Pegula as she looks to keep the momentum going.

Pegula holds to 15 and puts the pressure back on Karolina Muuchova.

Karolina Muchova has taken the opportunity to head off court before getting the decisive third set under way.

Seems like a sensible call from the Czech after the way this match has flipped on its head.

Jessica Pegula is a bundle of energy at the side of court, stretching, fiddling with her shoes and chatting with her coach.

The music is pumping around Arthur Ashe stadium too.

An eclectic mix from the DJ who is currently blasting out a dance version of Earth, Wind & Fire's 'September'. It's not as good as the original.

Muchova is back to save us.

Image source, Getty Images

Jessica Pegula hits a winner and Karolina Muchova responds with a drop shot into the open court.

Muchova sends a volley into the net and Pegula has two set points.

Pegula's backhand finds the net as one set point goes begging.

A double fault from Muchova gifts Pegula the game and the second set.

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

This next series of games is going to be very interesting.

Firstly, some of the crowd left thinking it wasn't going to go three sets.

The rest of this set and the third people will start piling back in and both athletles know they need to play their game to the best.

I don't believe in changing your game at this point. You have a strategy and you need to stick with it.

We're going to see who is better in this moment and under these conditions.

Image source, Getty Images

Jessica Pegula put that disappointment behind her very quickly by holding to love on her service game.

She is one game away from taking the second set.

Karolina Muchova's overhead shot and forehand goes wide.

She responds with a well-timed drop shot and then gets lucky as Jessica Pegula's shot hits the net cord.

Muchova wins the game with another sensational volley. The sixth seed will be gutted because she did all she could to reach it.

Karolina Muchova's shot hits the net and it catches Jessica Pegula off guard.

The American misses the court completely to gift Muchova the game.

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

Pegula turned right to her coach and was like 'I'm back!'

There's a lot of tension in both coaching boxes, though, and I'm not sure if they know what to say just yet.

Image source, Reuters

Jessica Pegula takes the fourth break point opportunity as Karolina Muchova nets.

What a turnaround, we have a match on our hands now!

Jessica Pegula's drop shot is easily read by Karolina Muchova who swipes a shot past her.

Muchova then fires an ace down the T at 110mph but her forehand is wide and we are back to deuce.

Karolina Muchova's forehand goes long before another one goes wide.

Jessica Pegula responds with a clean winner and she pumps her first.

But then... Muchova hits a sublime overhead volley and Pegula nets. She really shouldn't have missed that one.

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

Image source, Reuters

Jessica Pegula was trying to just be steady earlier and now she is hitting it just one foot from the baseline so Muchova can't get a full swing.

It's great when you've got time for a full backswing but it sends your balance off when you don't have it.

Pegula is finding that spot perfectly.

Karolina Muchova's drop shot goes just wide and Jessica Pegula leads for the first time in the second set.

The American looks rather relieved.

Karolina Muchova is suddenly looking nervous.

A backhand goes long but then Jessica Pegula nets.

Muchova's forehand shot goes long as Pegula saves break point.

Karolina Muchova hits her forehand into the net and then does the same with a drop volley to give Jessica Pegula a 0-30 advantage.

Muchova responds with her third ace of the match and Pegula's wild swing on the stretch makes it 30-30.

Muchova's forehand is long and Pegula has a break point which she takes at the first opportunity.

The number six seed is suddenly back in this match after converting the break point.

Image source, Reuters

Jessica Pegula gets her first ace of the match and then Karolina Muchova goes long.

Pegula keeps it to a single break and perhaps that will provide her with some much-needed confidence.