Russell Fuller
BBC tennis correspondent

It is quite something to think the US could have fielded three players ranked higher than the world number seven Jessica Pegula.

Coco Gauff, Amanda Anisimova and Madison Keys were all unavailable - and yet it is still a quality line-up.

Last year the US were beaten by Slovakia in the opening round of the Finals, and Emma Navarro had to save two match points against Yulia Putintseva on Thursday.

Had that match gone Kazakhstan’s way, the US may well have fallen at the first hurdle again.

That will certainly boost Emma Navarro's confidence.

It's not a comfortable hold and there's still too many groundstroke errors from the American, but it's a hold to 30 all the same.

Melanie South
Former British Fed Cup player on BBC TV

Navarro will be feeling the pressure. Kartal has really risen to the occasion. Navarro needs to take a few deep breaths and try to reset. You can see how she's feeling, it's not comfortable.

Sonay Kartal holds to 15 for a 4-1 lead. Who saw that coming?

Emma Navarro has only won four points since winning the first game of the match.

Sonay Kartal breaks again! She only needs one of her two break points, dictating the rally from the start and dragging Emma Navarro wide to open up a huge space on the court.

She's constructing points very nicely.

Wow. Sonay Kartal, on the baseline, brings out the sliced backhand drop shot to take a 0-30 lead. That's the shot of the day so far.

Emma Navarro nets a forehand. Two more break points for Great Britain.

That's more like it from Sonay Kartal.

She's found her first serve and is getting on top of more baseline rallies. A tidily struck forehand winner down the line is the pick of her shots in a routine hold to 15.

US captain Lindsay Davenport is emotionless at the side of the court.

Melanie South
Former British Fed Cup player on BBC TV

That will reignite Kartal's mindset that she needs to be more aggressive and keep on top of Navarro.

Sonay Kartal and Great Britain break right back!

An untimely double fault from Emma Navarro.

Boom. Emma Navarro, on one leg, hammers a cross-court backhand which Sonay Kartal can only return into the net: 15-all.

But, with a well set-up approach shot and a forehand error from Navarro, Kartal finds herself with two break points.

After eight or nine minutes and three break points, Emma Navarro finally gets the game over the line.

Too many missed first serves and too many forehand errors from Sonay Kartal in that opening game.

Uh oh. Sonay Kartal sends another forehand long.

We're going to a third deuce as Sonay Kartal defends with all of her heart. This opening game has been going on for seven minutes.

After a lengthy forehand exchange, Sonay Kartal spies a window to come into the net and buries a forehand volley for advantage.

However, a forehand error takes the game back to deuce. Navarro then drags Kartal back and forth across the baseline before hitting a volley winner of her own.

Break point number two.

Sonay Kartal gets herself out of trouble.

Sonay Kartal and Emma Navarro trade points to get up to 30-all, with American Navarro showing her intent early by climbing inside the baseline on a couple of occasions.

Kartal sends a forehand long to hand Navarro a break point.

Melanie South
Former British Fed Cup player on BBC TV

We heard from Katie Boulter that maybe this is their time to go through. She's been in the semi-finals a couple times, they are so dedicated.

From the start they have said they are here to win the title.

Right, we're about to get under way in Shenzhen.

Great Britain's Sonay Kartal has elected to serve first. Kartal has won each of her three BJK Cup matches since making her debut earlier this year.

However, world number 18 Emma Navarro is arguably her toughest test yet.

*denotes next server

BBC iPlayer

The first match will be getting under way shortly in Shenzhen and you can watch it live via this page and on BBC iPlayer.

Great Britain have reached a third Billie Jean King Cup semi-final in four years but face their toughest test yet against a United States team packed with talent.

To reach a first final since 1981, GB will probably need Katie Boulter to beat world number seven Jessica Pegula and Sonay Kartal to overcome world number 18 Emma Navarro.

Here's a look at how the two teams match up, including analysis from tennis correspondent Russell Fuller.