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

Krejcikova is looking a little resigned right now. Her body language has dipped considerably, she's looking a bit irritated and annoyed. Things are slipping away pretty fast here.

A comfortable hold to 15 for Jessica Pegula.

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

Obviously a slow start from Krejcikova in that first set but excellent from Pegula. I thought Pegula was returning really well, very deep to the baseline. She was also controlling the baseline exchanges, but when things were getting a little edgy, Krejcikova just wasn't able to capitalise.

Krejcikova will be very disappointed with that 4-3 game, that was the moment - a double fault, an error, handed the game across and Pegula's taken full advantage.

Image source, Getty Images

Jessica Pegula pounces on a tame second serve, powering her return down the line with Barbora Krejcikova motionless in the opposite corner.

Barbora Krejcikova looks a little flat-footed as she's pinned back behind the baseline by Jessica Pegula and plays a tired return into the net: 0-15.

Back-to-back double faults bring up three break points.

Barbora Krejcikova won't want to look at her first set serving statistics.

She struck three double faults, had a first serve percentage of just 40%, and only won 28% of points on her second serve.

She'll serve first in the second set.

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

Such a strange end to that game. Krejickova just went away from it - the double fault, the error, just when things were getting a bit edgy for Pegula. She was handed a gift in that last game.

Barbora Krejcikova sends a forehand long to hand Jessica Pegula the first set.

From 4-1 up, the American wobbled a little but she's now one set away from the last four and still yet to drop a set at this year's tournament.

From 15-30 down, Jessica Pegula turns back to what she's being doing best: hitting deep and dragging Barbora Krejcikova from corner to corner. The Czech eventually nets a return.

A forehand winner brings up set point.

This time Jessica Pegula seizes the break point. She'll serve for the first set.

Just when you think Barbora Krejcikova is getting into this...

She produces a welcome ace down the T and a big forehand winner while advancing on the net, and while a wide serve and down the line forehand combination doesn't come off (she was just wide of the tramline), it shows her attacking intent.

And then... the double fault. 30-40.

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

This year Pegula has had three title wins to her name, all of them on different surfaces, which is so impressive. It just shows you that she can adapt to different surfaces.

If Jessica Pegula had taken all of her break point opportunities, she'd have won this set 6-0 several minutes ago.

But now we're back on serve as Barbora Krejcikova pounces on a rare loose game from the American.

Thanks to a double fault from Jessica Pegula and a powerful deep forehand which her opponent can only hit long, Barbora Krejcikova has two break points.

Another huge hold from Barbora Krejcikova.

She saved a break point before perfectly executing a serve and volley off a wide serve to secure the game.

Break point saved. Jessica Pegula returns a hefty groundstroke from the Czech into the net.

An untimely double fault from Barbora Krejcikova.

Jessica Pegula is on top of Barbora Krejcikova's second serve, waiting right on the baseline in preparation for another attack on the net for 15-all.

And she pounces on another to bring up deuce, opening her racquet and pinging a cross-court forehand winner.

There's a vocal chorus of Barbora Krejcikova fans on Arthur Ashe, who create quite a racket whenever she wins a point.

The pair trade points for 30-all, giving the Krejcikova contingent plenty to cheer about, but Pegula, unruffled, wins the next two points to extend her lead.

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

That was an interesting rally. We are starting to see more of her tricks.