Abigail Johnson
Commentator on BBC Radio 5 Sports Extra and BBC Sounds

Pegula has been so maintained throughout this clash. How professional.

Barbora Krejcikova starts with a double fault - uh oh - before nailing a cross-court forehand for 15-all and following it up with an ace down the T. She's used that serve a lot.

However, Jessica Pegula responds with a forehand passing shot winner and then - you've guessed it - the Czech double faults. Match point.

Jessica Pegula holds to 15 and it's relatively event-free. She needed that.

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

This is getting a little tricky for Pegula and I wouldn't want to be in her shoes right now. I thought this match was going to be done and dusted.

This is what Krejcikova does, as soon as she gets a sniff of what's to come, she gets the job done.

Great combination. Barbora Krejcikova sends a second serve out wide and follows it up with a forehand winner down the line for advantage.

She completes the hold with another forehand winner.

Crunch time for Jessica Pegula. There's a lot of pressure on this next service game.

At 30-all, Barbora Krejcikova pounds in a second serve which Jessica Pegula can only play into the net. Where's she been hiding that?

However, a wild forehand from the Czech sends the game to deuce.

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

I can understand why Pegula is irritated because she played a good serve, Krejcikova had to serve a drop shot. The game took a turn after that and suddenly there is a different complexion on it.

What was I saying about this being a long way back for Barbora Krejcikova?

She pounces on a break point and if she holds her serve, things will start to get interesting.

Ooooh. That was some service return from Barbora Krejcikova, chopping the ball back across the net and leaving Jessica Pegula stuck on the baseline. She apologises - it didn't look like it hit the net chord to me.

Jessica Pegula is making hard work of another service game. Deuce.

Image source, Getty Images

Barbora Krejcikova sends a forehand long. Her groundstrokes have lacked control today.

Jessica Pegula now leads 4-1 in the second set. I know Krejcikova saved eight match points against Taylor Townsend the other day, but this feels like a long way back.

Jessica Pegula fires a return back onto the baseline and Barbora Krejcikova, backtracking, puts her shot just wide.

Barbora Krejcikova finds a first serve to save the first break point but then gives Jessica Pegula a look at her second serve. However, the American can't take advantage, sending a forehand into the tramlines.

Barbora Krejcikova can't string good games, or even good points, together. With a couple of netted returns, she's facing another two break points.

Abigail Johnson
Commentator on BBC Radio 5 Sports Extra and BBC Sounds

A woman who fended off eight match points in her last round probably won't be overly intimidated by the fact that Pegula currently leads 6-3 3-1.

If Krejickova can continue to tidy up her game, there could still be plenty of time left on Arthur Ashe Stadium in this first match of the day.

Jessica Pegula holds. After throwing away 40-0 and facing a break point, that was quite nerveless.

What a shot. Jessica Pegula was on her heels on the baseline when Barbora Krejcikova played a drop shot and followed it into the net. But the passing shot from the American is just too good.

A double fault from Jessica Pegula takes the game into a second deuce.

And she misses her next two serves. Advantage Krejcikova.

That might be the shot of the day from Jessica Pegula - a deft backhand volley which sails across the net at an acute angle with her opponent stranded in the back corner.

However, she nets three groundstrokes to give up 40-0 and take the game to deuce. Is Barbora Krejcikova about to steal a game?

Barbora Krejcikova was in total control of that game, leading 40-0 after nailing her first serves and using her backhand slice to get on the front foot in points and come into the net.

However, an excellent passing shot from Jessica Pegula and a netted return from the Czech bring it back to 40-30.

"Let's steal the game," yells a member of Pegula's box. With a hefty cross-court groundstroke, followed by a passionate pump of her first, Krejcikova shuts that down. She's battling.