It's been another rain-delayed day but here's what's happened in a few of the matches that have finished so far today.

Russian seventh seed Daniil Medvedev is safely through to the third round with a 6-1 6-3 7-5 win over American Sebastian Gorzny.

But it fellow Russian Andrey Rublev is out after the 23rd seed lost 7-6 (7-3) 2-6 4-6 4-6 against Spain's Daniel Merida.

Third seed Jessica Pegula beat fellow American Sofia Kenin 6-3 6-1, while Italian 19th seed Jasmine Paolini defeated compatriot Lucrezia Stefanini 6-4 6-1.

Daniela Hantuchova
Former world number five on BBC Radio 5 Live

I would be really humbled, I would sit down with my team and say 'OK, we need to change something big time'.

First of all, it was very obvious today that it was the serve. I feel like it needs to be cleared up because she was losing the rhythm and not using her legs. That's number one thing.

If I am Boulter, I would be on the practice court tomorrow. If she still wants to invest everything into her tennis and then she needs to be on the court.

Image source, Getty Images

Karolina Muchova was brilliant there but Katie Boutler never gave herself a chance.

The British number one served eight double faults and recorded 22 unforced errors.

Muchova earned seven break points in the match, with Boulter unable to save any of them.

Daniela Hantuchova
Former world number five on BBC Radio 5 Live

Unfortunately for Katie, it was not the best day in the office. Only 58 minutes played but Karolina had a lot to do with that because she so dominant and very solid with everything.

Daniela Hantuchova
Former world number five on BBC Radio 5 Live

At this stage what you're thinking and looking at the clock - 55 minutes, so 'OK let's just somehow push it to one hour' because I absolutely hated it when I was about to lose in less than one hour.

Karolina Muchova makes light work of her service game, holding to love with a delicate volley at the net, and she is now one game away from sealing her place in the third round.

Katie Boulter finds the line with a forehand winner before walking back to the baseline wearing a wry smile.

Her 21st unforced error of the match gifts Karolina Muchova break point and the Czech seventh seed takes it as she overpowers Boulter in a rally.

Boulter has yet to win any of her six service games.

We've passed the three-hour mark on Arthur Ashe Stadium and there's nothing to separate Ben Shelton and Hubert Hurkacz in this fourth set.

Both players have fended off break points and Shelton has just nudged in front thanks to a couple of serves upwards of 140mph.

The pair are certainly giving the fans their money's worth.

Katie Boulter has been inconsistent today but Karolina Muchova has been brilliant at times.

The Czech seventh seed comes through another game on serve, sealing it with an ace, before raising her first towards her coaching team in triumph.

A fist pump from Katie Boulter greets a strong first serve into Karolina Muchova's body which she can't return, but a double fault next point undoes the Briton's good work.

The game goes to deuce where Muchova fires a superb forehand winner, before Boulter double faults again.

This match is running away from the British number one.

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Katie Boulter needs to start this second set well after that disappointing first set and she does that by bringing up a break point.

It comes to nothing, as Karolina Muchova ups her game with some powerful serving to secure the hold, but that was more encouraging from the Briton.

Daniela Hantuchova
Former world number five on BBC Radio 5 Live

Unfortunately for Katie, she now has to think about how to get back to basics. Really move her feet a little bit more as it almost feels like she's in a little bit of panic mode.

I understand when you play someone of the calibre of Karolina, it's easy to be overwhelmed.

It's one-way traffic at the moment as Karolina Muchova brings up set point with Katie Boutler completely mistiming a volley at the net.

Boulter then puts a forehand into the net - her 15th unforced error of the set - and Muchova takes the first set.

Boutler is yet to hold on serve, losing all four service games in that first set.

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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.