Serena Williams beats Karolina Pliskova to reach semi-finals
American 17th seed wins 6-4 6-3 at Flushing Meadows
Argentina's Juan Martin del Potro through to semi-finals on Friday
Third seed beats John Isner 6-7 (5-7) 6-3 7-6 (7-4) 6-2
2017 champion Sloane Stephens knocked out by Anastasija Sevastova
Latvia's Sevastova through to semi-finals with 6-2 6-3 victory
Rafael Nadal plays Dominic Thiem in the last match of day nine
Extreme heat policy in place as New York temperature causes problems
*Stephens 1-1 Sevastova
Unforced error number five and then number six brings up 30-30.
I wonder how much Sev can see of Stevo's side of the court?
The Latvian then finds the net - break point already!
She saves.
Deuce.
Stephens 1-1 Sevastova*
The American finishes the job with a forehand into the corner.
Ones each.
Stephens 0-1 Sevastova*
Sev is now in the midday sun and Stevo has found some shade.
Are you a person who lies down the sun or prefers the shade? #bbctennis., external
30-0.
40-0 as Sev goes long.
*Stephens 0-1 Sevastova
The world number 18 holds after Stephens can't return an overhead.
Nice start to the match.
*Stephens 0-0 Sevastova
15-15 with Stevo pulling Sev from side to side.
The Latvian wins the next but then goes long with her forehand.
30-30.
What a rally and what a slice from Sev which plonks itself just over the net.
40-30.
*Stephens 0-0 Sevastova
*denotes next server
Stephens v Sevastova
We are about to get under way on Arthur Ashe.
Stephens v Sevastova
As you may or may not remember, these two players met each other at this stage last year.
The result? 6-3 3-6 7-6 (7-4).
So yes, as mentioned earlier this could be another three setter.
If it does then the players can have a 10-minute break between sets two and three because the Extreme Heat Policy has been applied as it's... extremely hot.
Image source, Getty ImagesFrom 18:30 BST onwards and on completion of this match we will have commentary on the first men's QF, between third seed Juan Martin Del Potro aka Delpo and John Isner aka 7-6 6-7 7-6 6-7 7-6.
Then at midnight BST we will have text comms on six-time champion Serena Williams against Karolina Pliskova, who beat her in the semis two years ago.
We will also have a report on the match between men's defending champion Rafael Nadal v Dominic Thiem, which will start at silly o'clock UK time.
Stephens v Sevastova
It's 32C BTW.
And here's Sloane Stephens, who's just had a pre-match chat: "They are tough conditions out there.
"I'll fight hard and play my game. Play steady and solid and do my best."
She's very straight bat is Stevo.
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I just don't know Pat, I just don't know.
Stephens v Sevastova
Image source, Getty ImagesDefending champion Sloane Stephens is getting stronger and stronger as the tournament has been progressing.
Last year's champ looked unflustered in her four wins to date - bar dropping a set against Kalinina - but now faces a potential three-setter against Latvia's 19th seed Anastasija Sevastova in the first quarter-final of this year's US Open.
The match is coming up in a few moments on Arthur Ashe. There is live BBC Radio 5 live sports extra commentary online.
Enjoy.