Novak Djokovic finds himself two points away from losing the first set to Zachary Svajda, but eventually holds serve.

Djokovic is down at 45% for first serves in so far - well below his usual level.

That is some response from Jiri Lehecka.

A second-set bagel gets the Czech on level terms over on court five.

Don't forget, Cameron Norrie will be next up on this court against Francisco Comesana.

British number one Emma Raducanu, speaking on Sky Sports: "I'm very pleased with how I played today. I had to wait two days to play this second round match so that kind of breaks the rhythm a little bit. I knew I was playing Janice [Tjen], who is a super dangerous opponent and she was playing extremely well coming into this. I knew she would easily put away any ball I put mid-court that wasn't necessarily good enough, so I'm really pleased with how I performed today.

"Janice [Tjen] is playing some really dangerous tennis at the moment. She has gotten through against some really tough opponents and she beat one of the top seeds in the first round, so I'm sure she will build and take a lot of confidence from this week. It was great to play against her and I look forward to the next time."

"It was really good to play in front of you guys on Louis Armstrong Stadium. I loved it once again so thank you so much."

On getting her 26th win of the season, the most victories she has recorded in a single year: "First of all, I think the consistency of doing good practice days every day has helped to build on that. I started to do that after the Miami Open and I was putting in some really good work, but I've also stepped up what I'm doing on and off the court in recent weeks.

"I'm really happy that I have those people in my corner over there and I'm really grateful for them. I'm just looking forward to building day-by-day and trying my best, that's all I can do. I'm putting a lot of trust in the work I'm doing behind the scenes so that's taking some of the pressure off."

Novak Djokovic has 15-30 on Zachary Svajda's serve but Svajda gets the better of a long rally with a rocket of a forehand winner down the line.

A backhand volley winner at the net wraps up a service hold to make it 5-4 to the American.

That was Raducanu's quickest ever Grand Slam win - exactly one hour.

She took 31 minutes to take set one and 29 minutes for set two.

Image source, Getty Images

I'm not sure Novak Djokovic will have had too many morning starts at Grand Slams in recent years.

It's worth remembering, also, that this is the first event he's played since losing at Wimbledon last month.

Still no breaks of serve in the first set.

Victory for Raducanu also makes her the first Briton through to round three in New York.

Can Cameron Norrie follow suit later today?

Jack Draper and Jacob Fearnley also remain in the men's singles draw.

Zachary Svajda has demonstrated in the first 30 minutes of this match that he will be a tough nut for Novak Djokovic to crack today.

Six winners and just the three unforced errors by the American so far, and he holds serve to love for a 4-3 lead.

Image source, Getty Images

Raducanu says she has "stepped up" with what she's doing "on and off the court" in recent weeks.

Well, it's paying off. Full quotes to come.

While Emma Raducanu was getting things wrapped up on Louis Armstrong Stadium, Novak Djokovic was in a touch of trouble facing two break points on his serve on Arthur Ashe Stadium.

But he finds a way to get himself out of danger and levels the first set at three games all.

Here we go.

Raducanu has match point after just one hour on Louis Armstrong.

It's hard not to get excited seeing Raducanu playing so well again in New York.

Tjen produces a couple of good winners to get a game on the board and prevent a second-set bagel.

Abigail Johnson
Commentator on BBC Radio 5 Sports Extra and BBC Sounds

Svajda plays a very pleasing classic game off the ground. He's incredibly sweet off both wings, the forehand and the backhand, and for his age, he's still in his early 20s, he's got a very cool head on his shoulders.

He's got lot of his experience on the ATP challenger tour to date. You wouldn't expect him to be a deer in the headlights, even against a 24-time Grand Slam champion.

Image source, Getty Images

Leon Smith
GB Davis Cup captain on BBC Radio 5 Sports Extra and BBC Sounds

This is tough for Janice Tjen. She played Veronika Kudermetova in the previous round, which was a big step up from what she had been doing previously as well, but she came through that.

That just highlights how well Emma Raducanu is playing right now. She is making this look easy, but it isn't.

Raducanu continues to chug along with some sublime serving.

She is making her first serve 76% of the time and 84% of the points behind her first serve.

A hold to love and she's in touching distance of the third round. Highly impressive.

Image source, Getty Images

It's been a good start by Zachary Svajda, who has looked comfortable since saving those two break points in the opening game of the match.

Wow. Relentless stuff from Raducanu and she takes the double break with a heck of a crosscourt winner.

There's not much sign of any issues during the points but she will certainly want this over with soon.

In his only previous second-round appearance at the US Open in 2021, Zachary Svajda took a set off Jannik Sinner in a four-set defeat by the Italian. Sinner was not quite the force then that he is now, but still a notable achievement.

So far, he has been unable to make any inroads into the Novak Djokovic serve. Another hold to love for the veteran Serb.

Image source, Getty Images