Former professional tennis player at Flushing Meadows
I would say Pliskova is favourite in this match but because Serena has spent so much time in Florida she is used to this humidity. That is a leveler.
Williams has only dropped one set en route to this stage, and that was against Simona Halep-slayer Kaia Kanepi in the last round.
World number eight Pliskova, on the other hand, has yet to drop a set. She was particularly impressive against Australian Ashleigh Barty in the last round.
Does the Czech player also have the edge over Williams having beaten her on this stage two years ago?
BBC Sport at Flushing Meadows
Karolina Pliskova doesn’t have to dig too deep cognitively to find positive memories of beating Serena Williams.
The Czech eight seed can take confidence from knowing she beat Williams in straight sets here at Flushing Meadows when they last met – in the 2016 semi-finals.
Martina Navratilova says revenge will be a motivating factor for Serena.
“Maybe Serena underestimated Pliskova, who played very well, and maybe she was surprised by the pace coming off Pliskova’s racquet,” she told BBC Radio 5 live.
“Pliskova can serve you off the court and she will have to try to do that today and keep the points short.
“But you know Serena is going to want to avenge that defeat.”
If anyone is well placed to discuss how good Serena Williams’ game is then it is Martina Navratilova.
The 18-time Grand Slam singles champion says Williams is answering some lingering questions from Wimbledon and looks “fantastic” in New York.
“She looked pretty good at Wimbledon but had an easier draw getting to the final so there was a lot of doubt,” Martina told BBC Radio 5 live at Flushing Meadows.
“Still she got to the final but I think her lack of match play and lack of competition against top players showed against Angelique Kerber.
“Here she has had some tougher matches against tougher opponents and has been playing better and better. She looks extremely confident.
“I’ve been impressed by her footwork seems to be getting set for her shots and hitting well.”
We are back at Arthur Ashe as Serena Williams continues her quest for her seventh US Open title.
Who stands in her way? Her 2016 nemesis Karolina Pliskova.
We have live text commentary coming up and audio commentary on BBC Radio 5 live sports extra for what promises to be a fascinating encounter.
Right. The action on Ashe is taking a break so we will too.
We’ll be back when Serena Williams and Karolina Pliskova begin their quarter-final just after midnight in the first match of the night session.
See you shortly.
Here’s the winner Juan Martin del Potro: “I’m so happy to reach another semi-final in my favourite tournament that is very special to me. Beating John in these kind of matches – it’s epic. We were both tired in the end and I survived with my serves during the match.
On his 10-minute break between the third and fourth sets due to the extreme heat policy:
“During the 10 minutes I had a shower, re-taped my ankles and a lay down on table – I didn’t want to come back again.
“The heat was strong, but this crowd and this energy…”
On his small group of hardcore supporters:
“If I meet my supporting group it might be dangerous! I’ll stay in my hotel and let them walk around the streets. They’ve made the effort to come up from Argentina – flights, hotel and beers.”
Del Potro will play Rafael Nadal or Dominic Thiem in the semi-finals.
Those two play later in the night session.
The men’s semi-finals aren’t until Friday so the former champion has time to recover from those fatigue issues.
What a guy. Does anyone dislike Juan Martin del Potro? If you do, you’re wrong.
He’s asked what he did in the 10-minute break between sets due to the heat rule.
“I didn’t want to come back again!” he laughs.
John Isner gets a great ovation from the crowd as he makes his way off court. His wife is due to have a baby soon. Every cloud.
Del Potro looks like a happy school boy as he waits for his post-match interview.
Juan Martin del Potro is back in the semi-finals at the US Open! John Isner dumps another into the net and the Argentine is beaming. The former champion is right in with a shot this year.
Both men come together at the net and embrace.
Del Potro then stands in the middle of the court with his arms aloft and looks to the skies.
Here we go.
Three hours and 30 minutes in, Juan Martin del Potro has match point.
It’s stand and deliver stuff from both men. They don’t want to run. If it’s there to hit they’ll hit it. If it’s not they’ll not waste any energy trying.
Double fault from Isner. Both men are limping towards the finish line. Del Potro is on the home straight though. Isner hasn’t even made it to the final bend.
Del Potro is having his thighs rubbed frantically by the trainer. I’m no doctor but it looks like fatigue.
Isner must hold serve here or he’s out.
All is not perfect for Del Potro but he gets through. He bangs a few more heavy forehands but hardly moves when a counter-punch from Isner flies by.
Here comes the trainer again.
Regardless, Del Potro is one game away from the semi-finals.
A 129mph serve from DelPo. His fans can breathe a little easier.
Now another thunderbolt.
Now then. Del Potro is hardly moving at all at the back of the court. Could this be something serious? He already has the service break so this game doesn’t matter too much.
This next service game does. Was Del Potro just saving energy?
Ooooh. I assumed the trainer would be for John Isner who was struggling with cramp in that last game but it’s not. It’s for Juan Martin del Potro.
It seems to be something to do with DelPo’s leg. The trainer tells the umpire he’ll be back at the next change of ends. There might not be one.