Karolina Muchova is stretching, arms above her head, trying anything to alleviate the discomfort in her side.

She puts in an unreturned serve from the opening point - then gets a mini-break as Gauff finds the net!

Emily Salley
BBC Sport at Wimbledon

To a tie-break we go. How are the nerves?

The atmosphere is tense on Centre Court.

Karolina Muchova is wincing with every step now - this game has lasted two and a quarter hours in 30 degree heat. A real endurance test.

Coco Gauff meanwhile seems to be moving completely smoothly, however is being made to work as Muchova shows impressive adaptability with her returns.

But as Muchova goes wide, we will have the match tie-break.

Anne Keothavong
Former British number one on BBC One

It's really hard to even pick between these two. It seems to be Muchova who physically is looking to be struggling a bit more.

She was moving gingerly between points. Looking fatigued, touching her abs.

Image source, Reuters

If Gauff wins this game, we will have a match tie break - first to 10 points.

Gauff to serve.

Marion Bartoli
Former Wimbledon champion on BBC Radio 5 Live

That was an incredible hold from Karolina Muchova.

World class tennis from both players.

Image source, Getty Images

Naomi Cavaday
Former British tennis player on BBC One

If you are Muchova, why are you even giving Coco Gauff that many backhands to play?

Coco Gauff is turning it on when it counts. She wins a rally with a magnificent backhand into the far left corner of the court, bringing the crowd to their feet.

Karolina Muchova is giving Gauff too many chances to play with her favoured backhand, could it prove costly?

For now though, Muchova is going with Gauff - a lengthy rally is won by the Czech with a volley into the open court, but she then doubles over and holds her ankle. Hopefully nothing serious - she also seems to be holding her abs and wincing.

Apparently nothing serious, as a placed forehand winner moves her 40-30 ahead. And a backhand to the baseline secures the hold.

Image source, PA Media

British duo Andy Lapthorne and Greg Slade have been beaten in their quad doubles semi-final by Sam Schroder of the Netherlands and Jin Woodman of Australia.

The number two seeds were 6-4 6-1 winners on court 14.

Lapthorne will play Schroder in the semi-finals of the quad singles.

If Coco Gauff is feeling nervous about being in unchartered Wimbledon territory, she is not showing it.

She holds to 15, and on we go.

Tracy Austin
Two-time Grand Slam champion on BBC One

Now it is going to be about who manages the nerves. Who can execute under the tension.

Sometimes it clouds your shot selection.

Annabel Croft
Former British number one on BBC Radio 5 Live

I don't know how Karolina Muchova got through that game. She held strong there.

It is nip and tuck and Muchova did a good job of holding the nerves.

Image source, Getty Images

If Karolina Muchova breaks, she will reach only her second Grand Slam final - having reached the final of Roland Garros in 2023, where she lost to Iga Swiatek.

Coco Gauff is leaving it all out there, pulling out a superb chipped shot and Karolina Muchova can only dish up an easily smashable winner for Gauff in return.

But Muchova collects herself, and a tense forehand from Gauff means we go to deuce again.

Gauff takes a big risk with a large cross-court backhand - and HawkEye shows it is out by barely a millimetre! A wry smile from Muchova, she knows she's a bit lucky there.

And with an unreturned serve, the Czech holds!

Karolina Muchova pies an 80mph second serve to Coco Gauff's favoured backhand - but the American puts it in the net!

Deuce, and a yell of anger from Gauff.

Suddenly it is Karolina Muchova who is having to work for every point on her serve. It feels like the momentum has swing once again in this match, back towards Coco Gauff.

Muchova sends a cross-court backhand wide, 15-30. But she moves back level with an excellently played serve and volley.

But after a weak second serve, Muchova is forced into sending a backhand well long. Break point Gauff...

Tracy Austin
Two-time Grand Slam champion on BBC One

Coco Gauff at the net has been absolutely remarkable.

She has made it very uncomfortable for Muchova to hit clean passes.

Marion Bartoli
Former Wimbledon champion on BBC Radio 5 Live

Coco Gauff is willing to make the move forward and play bold tennis.

We know her for incredible skills from the back of the court but she keeps coming to the net and winning points.

Quite extraordinary.

If Coco Gauff breaks here, she will serve for a place in the Wimbledon final.