Back on serve. More first pumping from Daria Kasatkina. She takes the second of those break points. The Centre Court atmosphere is building. They like what they see from the 21-year-old Russian.

Angelique Kerber's one blip in this match came when she lost her break of serve at a similar stage in the first set.

She isn't going to do it again is she?

Out of nowhere Kasatkina has three break points...

Sonia Oxley
BBC Sport at Wimbledon

Angelique Kerber is four-time Grand Slam champion Kim Clijster's pick as the woman who can challenge Serena WIlliams for the title here.

"She's left-handed, she’s a great mover, she can get a lot of balls back," the Belgian said.

Williams needs to get past world number 52 Camila Giorgi this afternoon to reach the semis, which Clijsters says is an interesting match-up.

"Giorgi is always a tricky player, she brings so much energy out on court," she said. "But I think that still Serena on grass has better weapons, Giorgi also has the extreme grips – it might get a little bit fast for her in the rallies but anything is possible."

Image source, Reuters

Kim Clijsters
Four-time Grand Slam champion

You want to feel comfortable out there and I don't think Dominika Cibulkova is the type of player who needs to change her game.

She will only be able to play her best level which is from the baseline. Maybe she can concentrate on getting more of her first serves in.

Jelena Ostapenko takes the first set. She won nine points in a row, including two successive aces in the final service hold.

Dominika Cibulkova hasn't played badly but has just dropped her first set of the tournament.

Daria Kasatkina isn't giving up. Another big punch of the air as she comes out on top of another testing rally. The Russian is fiery. She stays in touch.

Here's a break point opportunity for Del Potro which he takes to move to within one game of victory.

Del Potro had been looking a bit tentative on the forehand side but the pressure on Simon forced him to go for too much.

This one from earlier was probably the rally of the morning so far...

John McEnroe
Three-time Wimbledon singles champion on BBC TV

I don't think Kasatkina has been disciplined enough.

When she gets a short ball she looks like she is not sure what to do. She needs to be aware of consequences when she hands counter-puncher like Kerber the opportunity to attack.

The legs really aren't moving yet and the focus not quite what I would like to see from her.

More efficient play from Angelique Kerber. A hold to 15.

The break is consolidated.

Here's the moment she clinched the first set...

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Florence: Peter Fleming and John Lloyd. Proper commentators, unlike some I could mention. I don't want celebrities, I want good commentary!

Once again Jelena Ostapenko's returns are just too good for Dominika Cibulkova. She breaks for the third time and will now serve for the first set.

Image source, AFP

Wild from Kasatkina again. One framed shot out of the court and another way long of the baseline. Kerber breaks at the start of this second set. There is little reaction from the Centre Court crowd. They want a third.

Kerber has been very, very clinical.

Image source, AFP

Daria Kasatkina's baby face looks a little grumpy despite showing off the trick shots. She's left sprawling by a Kerber passing shot that brings up break point.

A rare error from Kerber. Deuce.

Mark Petchey
BBC Sport tennis commentator

It is still difficult to pick a winner here.

However, I would say that even if Del Potro gets through, unless he has an amazing serving day against Rafa, he will struggle in the quarter-final.

Image source, Reuters

Hot dog! The 'tweener' - where a player hits the shot back through her legs with her back to the net - is one of Daria Kasatkina's favourite shots. A Kerber lob gives her a chance to show it off on Centre Court but this one clips the tape. A* for effort though.

Kerber holds.

That was a much more routine service game for Dominika Cibulkova. It is the first one of the match where Jelena Ostapenko didn't get much of a look in.

Cibulkova celebrates with a huge roar and a fist pump - jumping up and down and looking towards her box.

The former French Open champion has been returning brilliantly. This was one of her breaks earlier in the set.

Here are the stats from the first set on Centre Court. Just two unforced errors from Angelique Kerber in nine games compared to 13 from her opponent .

There is no doubting Kasatkina's talent though. She shows more great touch to flick away a shot at the net on her way to holding at the start of the second set.

It sounds like the crowd are going to get behind the Russian.

Tracy Austin
Two-time Grand Slam champion on BBC TV

Kerber was so much cleaner in that first set.

Kasatkina needs to contain that enthusiasm. She has got such a huge upside, talent levels off the charts. It is just about putting the puzzle pieces together.

Dan: Halfway through the 1st set in the first two quarter finals and the level of play is amazing. I knew we were in for a treat from these matches

Jason: Kasakina has the ability and game to win multiple slams. She’s like a female Roger Federer

Mark Petchey
BBC Sport tennis commentator

The backhand down the line is not working for Simon at the moment.

But I do love his ability to play the ball hard and then rein it back in.