Harry Poole
BBC Sport at Wimbledon

Another topsy-turvy Coco Gauff classic, which certainly had the Centre Court crowd engrossed here.

She made four double faults and 17 unforced errors in the first set, but just three double faults and 15 unforced errors across the remainder of the match.

Gauff raises her arms aloft after coming through that tricky challenge against American number one Jessica Pegula, which should give her plenty of confidence going forward on a surface she hasn't exactly thrived on.

Jan-Lennard Struff gets on top of a baseline exchange, hitting flat and driving Jannik Sinner back until the top seed makes an error. 15-all.

The pair trade points for 30-all.

Sinner angles a second serve which Struff can only chip back into court, opening the door for a couple of booming Sinner forehands, and closes out the hold with an ace.

Pat Cash
Former Wimbledon champion on BBC Radio 5 Live

That was a good effort because Gauff was having all sorts of timing issues in that first set and the majority of that second set.

Once her first serve clicked, boom.

It's incredible how many times she's not played well but is somehow able to get through the match.

Coco Gauff came in as the seventh seed. The American is now the highest seed remaining in the women's singles draw.

She'll face the winner of Naomi Osaka and Karolina Muchova in the semis.

Tracy Austin
Two-time Grand Slam champion on BBC One

Image source, Getty Images

This is a big deal.

Wimbledon was Coco Gauff's breakout tournament. I remember the 'Coco-mania' when she was just 15 years old, after she beat Venus Williams to get to the fourth round here.

She has struggled since then, but she has just fought so hard to work on her serve and her forehand. They both got better with each set today.

Double fault. 0-30.

Jan-Lennard Struff goes big down the T and misses his first serve by several feet. But his second serve is good and he works his way into the net to put away the backhand volley.

He pounds down a 121mph second serve to level the game and then finally finds a couple of first serves to come through the hold.

Pam Shriver
Five-time Wimbledon doubles champion on BBC Radio 5 Live

What wears on you mentally is the speed of Coco Gauff. You feel as the match goes on, you have to be so precise and hit your spots so unbelievably well. Especially when she's cleaned up like she has.

Coco Gauff won the mental game out there.

Sam Smith
Former British number one on BBC One

Once again, Coco Gauff is the comeback queen!

For the fourth match in a row, she has won in a deciding set. Her player box must be utterly exhausted, but she is through to a first Wimbledon semi-final.

Look what it means!

Jessica Pegula goes long with a forehand and Coco Gauff has match point...

Jannik Sinner breezes through his latest hold and strides back to his chair.

Pam Shriver
Five-time Wimbledon doubles champion on BBC Radio 5 Live

The elevation of Coco Gauff's game after losing the first set has been magnificent.

Tracy Austin
Two-time Grand Slam champion on BBC One

Jessica Pegula is playing about the same tennis set-to-set, plus or minus a touch, but Coco Gauff has been able to elevate her groundstrokes to a tremendous level from where she was in the opening set.

In the first set, Gauff was at 67mph average on the forehand but she has now gone up to 72mph. She keeps increasing her top spin and she is getting full control of rallies.

Another stunning rally and Jessica Pegula gets to Coco Gauff's drop and whips a passing shot... millimetres wide!

Gauff stands firm on serve despite Pegula showing she doesn't lack for fighting spirit either.

I'm certainly not ruling out another twist - or two - before this one is done.

Image source, PA Media

Emily Salley
BBC Sport at Wimbledon

Hi Harry, thanks for getting in touch! It is pretty hot out on Court One at the minute and Sinner has had problems coping with stifling conditions in the past, but it doesn't really seem to be impacting him too much today.

The top seed just hasn't found his top form at these Championships yet, but he's still good enough to strike decisively in the key moments.

Image source, Getty Images

Very stylish! Jannik Sinner goes for a lob but a leaping Jan-Lennard Struff bangs down a backhand smash winner.

A second-serve ace secures the hold.

Jan-Lennard Struff and Jannik Sinner get locked in a baseline exchange, neutralising one another until the German puts a cross-court forehand into the tramlines. Back to deuce we go.

Pam Shriver
Five-time Wimbledon doubles champion on BBC Radio 5 Live

Who's going to respond best under this immense pressure?

At the moment, it looks like Coco Gauff.

Greg Rusedski
Former British number one on BBC Radio 5 Live

Sinner is getting the job done but he hasn't hit his top level yet.

If he does get through, he cannot play like this. But for now, he has to focus on winning this.

Image source, Getty Images

Jannik Sinner misses a forehand. Not to be this time.