Karolina Muchova has taken control of this match now as she races into a 40-0 lead with some fine first serves.

The Czech seventh seed then seals the game in style as she finds a forehand winner past a stranded Katie Boulter.

Muchova is one game away from taking the first set.

After missing a break point on Hubert Hurkacz's serve, Ben Shelton is put under pressure on his own. But after a couple of deuces, he finds a way through - much to the delight of the partisan crowd who are backing the home hope.

Karolina Muchova continues to return well as Katie Boulter delivers more unforced errors on serve and the game ends up running away from the Briton.

Muchova opens up two break points before Boulter puts a forehand long and the Briton now has a lot of work to do to get back in this first set.

Image source, Getty Images

Daniela Hantuchova
Former world number five on BBC Radio 5 Live

Katie had a big chance with that second serve return and it seems like both players are still trying to find their rhythm.

Karolina Muchova looks to have the game in the bag but serves a double fault, before going tamely into the net as the game heads to deuce.

The Czech seventh seed recovers well though, as she takes the game with a whipping forehand which Katie Boulter can't get back into play.

That's the first hold of serve so far in the match.

Karolina Muchova plays the shot of the match so far with a forehand which just clips the backline, bringing oohs from the crowd in New York.

Muchova then hammers a forehand winner to bring up break point, and takes it as Katie Boulter can't control her backhand.

Three games, three breaks so far.

Image source, Getty Images

Daniela Hantuchova
Former world number five on BBC Radio 5 Live

Boulter has to take the initiative because when Karolina has the time to create her wonderful magic, and she can do pretty much anything on the court as we've seen, she is very hard to stop.

So Katie has to start being very aggressive.

A deep return from Katie Boulter forces Karolina Muchova into a mistake, prompting a fist pump from the Briton.

Muchova then overcooks a forehand and Boulter now has two break points of her own.

She makes the most of them to break back immediately with a smart forehand down the line.

A shaky start from Katie Boulter as she plods a couple of forehands long before serving a double fault.

Karolina Muchova has two early break points and she makes them count as Boulter fires long again.

A grimace and shake of the head from the British number one tells us she's disappointed with that.

Ben Shelton takes the third set. He never really looked like giving that tie-break up and he's helped along the way by some really poor misses from Hubert Hurkacz.

The Pole heads off court for a re-set, while Ben Shelton chats away to his team. His dad, a former player himself, has got a beaming smile on his face.

Image source, Getty Images

Katie Boulter is looking to become the first Briton to reach the third round at the US Open this year.

The British number one beat wildcard Carol Young Suh in three sets on Sunday to set up the tie with Czech seventh seed Karolina Muchova.

Muchova, who reached the Wimbledon final just under two months ago, eased past Austria's Sinja Kraus 6-3 6-0 in the first round.

The pair have met only once before, with Muchova winning in straight sets at the Miami Open earlier this year.

A double fault sets Hubert Hurkacz off on the wrong foot and Ben Shelton capitalises, opening up a 3-0 lead with a stunning drop shot.

American Ben Shelton is the eighth seed and one of the favourites, but he's been handed a difficult draw. He opened his US Open with a four-set win over Tallon Griekspoor, the former world number 12, and now he's up against Hubert Hurkacz, who has been ranked as high as sixth in the world.

It's one set apiece and it looks like we're in for a tense end to this third set as the Pole holds serve for a 6-5 lead.

Laura Robson
Former British number one on Sky Sports

On Katie Boulter's three-set victory against wildcard Carol Young Suh Lee in round one...

She was nervous but I think it was tough though. You're playing an opponent you don't know too much about, you know that you're the favourite in this situation but I liked how she came out and reset after that second set.

She had such intensity in the third and got the early break and from then never looked back. She just went for her shots but with restraint which is such a big thing for Katie - she can hit a big ball but it's just building the point out is something she's been working on for a while now.

Image source, Getty Images

Play on the outside courts is suspended until at least 21:00 BST, so we're going to turn our attention to the show courts.

Brit Katie Boulter has been moved from court 17 on to Louis Armstrong for her second-round meeting with seventh seed Karolina Muchova.

• Brit Jan Choinski lost to Botic van de Zandschulp in straight sets in their delayed first-round meeting.
• American third seed Jessica Pegula dropped just four games as she eased into the third round with victory over Sofia Kenin.
• Men's seventh seed Daniil Medvedev also advanced to the third round in straight sets, beating Sebastian Gorzny.

We were about to get under way on court five with Britain's Fran Jones set to resume her first-round match against Poland's Magda Linette after it was suspended on Tuesday because of rain.

The players had just finished their warm-ups when it started to rain again, so the match has been delayed further.

Hopefully this rain won't stick around for long...

Well, that came out of nowhere. Thought I was going mad when both players headed to their chairs at 40-15.

A few hardy souls have stayed in position under umbrellas in the stands but most spectators are dashing for cover.

While we wait, let's recap what's happened so far on day four...

At 15-all, Tomas Martin Etcheverry finds an ace and then gratefully accepts a forehand error from Jacob Fearnley.

Two set points!

But then... rain.

Jacob Fearnley is on course for the first love hold of the match but Tomas Martin Etcheverry has other ideas.

He positions himself for a forehand off a wide serve and is duly rewarded, the ball sitting up nicely for him to wallop at shoulder height for a down-the-line winner.

He pulls another point back before Fearnley closes out the hold with an ace.