Yup, you've guessed it. A big first serve from Jannik Sinner isn't returned into play.

Jan Lennard-Struff rattles through two quick points of his own.

Greg Rusedski
Former British number one on BBC Radio 5 Live

Sinner is serving magnificently, that's what is keeping him out of trouble.

More first serves from Jannik Sinner, including an ace out wide. He's two points away from a two-set lead.

Greg Rusedski
Former British number one on BBC Radio 5 Live

It's been a very unusual from Jannik Sinner today. A lot of unforced errors from the back of the court, weak forehand.

He doesn't look like the supreme force Jannik Sinner that we're used to

One thing that has been impressive from him today is his service game.

Jan-Lennard Struff plants a routine backhand into the net. Jannik Sinner offers a shake of the racquet. He has the mini-break.

Struff stays in touch with some sharp net play.

Jannik Sinner responds with two mighty first serves of his own. Jan-Lennard Struff gets a racquet to both but can't put his returns in court.

Jessica Pegula brushes off the disappointment of dropping that second set with a comfortable hold to start the third.

Harry Poole
BBC Sport at Wimbledon

Jessica Pegula will be kicking herself. Having had the chances to put herself on track for a straight-set win here, she has gifted Coco Gauff a route back into this match.

Gauff skips in celebration and clenches her fist as she strides to her chair, while Pegula has he head bowed as she walks over from the baseline. Now it really is anyone's match.

Jan-Lennard Struff opens with an ace.

Jannik Sinner holds to 30 with an ace down the T.

These two exchanged breaks in games three and four of the second set and both failed to convert break points later on - Jan-Lennard Struff missing out on set point. There's only one way to settle this: tie-break!

Image source, PA Media

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

This is why Coco Gauff has won two majors. She doesn't mind winning ugly.

Andrew Castle
BBC Sport tennis commentator on BBC Two

Both players are in the trenches in this one, aren't they? It has been a kind of old-school match.

Jan-Lennard Struff has come out here and used his enormous experience. He knew full well that he didn't want this to be a pretty looking tennis match because he would lose it. He is just taking the ball and hammering whenever he can. Jannik Sinner, on the other hand, is doing what he can to just keep his nose in front.

There is one great player on this court and the other player is just an unbelievably good workman. It is quite the match-up.

We're going the distance, folks - and you were warned!

Coco Gauff battles back from 0-30 down and hammers an ace down the middle to take the second set.

Things become so much simpler for her when that serve is in even halfway decent order.

Jessica Pegula will rue not taking her chances early in that second set.

Image source, Getty Images

A monstrous forehand return from Coco Gauff helps up bring up three break points - her first of the set...

And a double-fault from Jessica Pegula gifts it to her old doubles partner!

Gauff clung on early in this set, breaks and will now serve to level the match.

At 30-all, Jan-Lennard Struff nets a first serve. He goes wide on his second and wallops Jannik Sinner's deep return for a down-the-line winner.

An ace completes the hold. Sinner will once again have to serve to stay in the set.

Image source, PA Media

Pat Cash
Former Wimbledon champion on BBC Radio 5 Live

Both players have got their tactics right. It's just no one has been able to string a lot of points together.

Image source, Getty Images

Greg Rusedski
Former British number one on BBC Radio 5 Live

This is where Sinner is so good in his service accuracy, it gets him out of trouble.

Andrew Castle
BBC Sport tennis commentator on BBC Two

Those targets become smaller as the match becomes closer. Jannik Sinner just couldn't hit it.

As a reminder, he had the break in this second set but Jan-Lennard Struff is hanging around, as he has done throughout this tournament.

Coolly done by Coco Gauff to keep this second set on serve.

Down 0-30, the pressure was on but there were no signs of nerves this time from the 22-year-old.

A 122mph ace down the middle takes it to 40-30 and then, with a little bit of help from a generous net cord, she converts game point as Jessica Pegula fires into the net.

Image source, Getty Images