Goodness me.

Another break point comes and goes but Pegula's forehand down the line drops the wrong side.

Chance number four for Boulter. We go again.

A whipped forehand to the corner of the court saves break point before Pegula moves to within one point of taking the court.

But back-to-back ripping forehand returns bring up a third chance for the Brit.

Third time lucky?

Melanie South
Former British Fed Cup player on BBC TV

I feel Boulter could have done more on the second serve return. They are the fine margins against players in the top 10.

Pegula is on the defence and can't get her forehand over the net. A second break point for Boulter.

A double fault from Pegula just offers Boulter a little glimmer of hope at 15-30 then the Brit brings up a break point but can't punish Pegula with her forehand return.

Deuce.

Melanie South
Former British Fed Cup player on BBC TV

Really positive from Katie Boulter. She's using her team a lot, a lot of eye contact. She's got belief.

Boulter has admitted problems on serve in the past few months but no such problems on show in that service game as she takes the hold to love.

Fran Jones may not have appeared in Great Britain's BJK Cup Finals campaign so far but she is certainly embracing her role as number one cheerleader...

Image source, Getty Images

Boulter apologises for a net cord that drops in her favour but that is the only point the Brit takes off the Pegula serve.

A solid hold for the American.

Boulter does well to save the break point and move ahead to take the hold.

A break of serve would not be ideal at this point in the match.

Melanie South
Former British Fed Cup player on BBC TV

Pegula has came out here with real purpose. She's not allowing Boulter to lead the pace of this match.

Pegula earns a break point in Boulter's opening service game but the Brit saves it with an overhead smash and lets out a big roar.

The Brit is trying to get herself going in this match.

Pegula gets her first game on the board with a hold to 15.

Solid ball-striking from the American.

Off we go then.

A must-win match for Great Britain and Boulter. Victory for the US would give them an unassailable 2-0 lead in the tie.

* denotes next server

It has been a difficult season on the tour for British number two Katie Boulter, and an opening-round loss at the US Open saw her drop out of the top 50.

But she has always been impressive when representing her country, winning 17 of 23 matches played for Britain.

Her latest appearance against Japan's Moyuka Uchijima sealed GB's place in the semi-finals.

But up against American Jessica Pegula, she faces one of the most consistent players on the tour.

The world number seven has not dropped out of the top 10 for three years, reaching the semi-finals of the US Open last month.

Pegula lost her singles rubber to former Wimbledon champion Elena Rybakina in the quarter-final against Kazakhstan.

However, the 31-year-old recovered to win the deciding doubles match alongside Taylor Townsend as the US pursue a record-extending 19th title.

Slightly earlier than I suggested, apologies. Boulter and Pegula are out to warm up for match two of this semi-final tie.

We'll be back in around 15 minutes for the second singles match where British number two Katie Boulter takes on world number seven Jessica Pegula.

It's a must-win match if Great Britain are to stay in this semi-final tie against the United States.

Emma Navarro speaking after her win over Sonny Kartal: "I had a ton of support from the ladies in my team. I feel a ton of pride playing for my country, it means the world to me to have the American flag on my chest.

"I was hearing you guys cheering me on. Great Britain was pretty loud in this match, I needed all the help I could get. Thanks for cheering me on."

Russell Fuller
BBC tennis correspondent

That was Sonay Kartal’s first-ever experience of defeat in a Billie Jean King Cup match, after three wins out of three in this debut season.

She was very good, aggressive throughout and only faded slightly in the final few games of the match.

Emma Navarro has had a stressful week, but after saving match points to beat Yulia Putintseva in the quarter-finals, showed again what an asset she is to this American team.

A brilliant, resilient performance from Kartal. She will be gutted to have lost that after taking the first set. Her first BKJ Cup defeat.

Navarro steps up to the microphone for her post-match interview wearing a USA headband.