There's plenty of fight still in Katerina Siniakova!

The doubles specialist digs in to hold from 30-30 and level the second set from 5-3 down.

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Naomi Osaka hasn't given much away out on court today, but a quick glance to her team after her latest miss suggests she's just starting to get a bit frustrated here.

But, from 30-0, Siniakova makes a couple of misses to bring Osaka into contention and two points from victory.

Harriet Dart is edging the rallies so far but she can do nothing about that as Marie Bouzkova nails a perfect drop shot.

The Czech 25th seed seals the game as Dart is unable to get a forehand over the net.

Naomi Osaka concedes the game as she nets a forehand, and a first chance to book her place in the third round slips from her grasp.

Four consecutive breaks of serve, and it's very difficult to call which way this is going to go.

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Goodness me this is a scrappy end to this second set.

For a fourth straight game we have break points, and two chances for Katerina Siniakova to deny Naomi Osaka as she serves for the match.

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It's a confident start from Harriet Dart who has settled into her stride as she wins a couple of rallies from the baseline.

Dart seals the game as she steps into the net with Marie Bouzkova unable to find a way past.

Abigail Johnson
Commentator on BBC Radio 5 Sports Extra 2

Katerina Siniakova has been scrambling, and she has not been able to put all her colours out on court today against the former world number one, Naomi Osaka.

Just when it looked as if Katerina Siniakova had gained a foothold, Naomi Osaka fires back to reach three break points.

Can the Czech go again here?

Siniakova sees off one break point but concedes the second. That will be such a huge disappointment after waiting so long to finally make a breakthrough of her own.

Osaka will serve for a place in the third round.

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Harriet Dart is due on Court 11 shortly against Czech 25th seed Marie Bouzkova.

Dart is one of only two remaining Britons left in the singles at the US Open, alongside Fran Jones, who plays later today.

Dart and Bouzkova have only met once before, with the Briton winning in three sets at Eastbourne in 2024.

After a third deuce, Katerina Siniakova has a second break point.

Can this be her moment? It is!

Well, I'm not sure many saw that coming when Naomi Osaka made the breakthrough in this set, but a few unforced errors allow Siniakova back into it. Game on...

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Not so fast. Katerina Siniakova has a mountain to climb here, but she is still scrapping away as we hit the hour mark on Arthur Ashe Stadium.

The Czech has not managed to create a break point yet, but reaches deuce here as Naomi Osaka hits long.

And now Siniakova will have her first opportunity following a great return!

A bounce off the net cord allows Katerina Siniakova the time to pick her spot with a forehand to see off the second of the three break points.

But there is nothing she can do about that!

Despite her best efforts, Siniakova is sent sprinting from side to side as Naomi Osaka dictates from the baseline before eventually firing in a winner to take charge of the second set.

The two-time champ can see the finish line now.

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Katerina Siniakova is really annoyed at herself as she falters on a forehand and falls 0-30 down.

Yet another polite reminder from the chair umpire asking people to show some courtesy to the players and remain quiet during points. Sigh.

Back on the court, this looks like it could be starting to unravel for Siniakova. Three break points.

No concerns for Naomi Osaka in her latest service game.

Can Katerina Siniakova continue to hang in here? She's back down in the trickier, sunny half of the court as she attempts to level at three games apiece.

This could be where Osaka looks to strike...

Katerina Siniakova lets out a cry of frustration after double-faulting for the first time in this set, but fifth today.

Fortunately for the Czech, she is already 30-0 up when that happens. Osaka outmuscles her opponent to close to 40-30, but Siniakova lands a first serve to stay in touch.

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Iga Swiatek, speaking on the Grandstand court after her victory: "I remember how she [Podoroska] played.

"We basically played in one of my important tournaments. I knew how her ball would feel on the racquet. A lot can change in six years, so I was preparing the same as I was before any other match.

"I am here with a better feeling probably than any other Grand Slam this year. I am happy to have another opportunity to play here."

On her Lego hobby: "It is a small set, so I think I will be done pretty soon.

"I have my competition on the court, but Lego I can do slowly, just relaxing. I only do 18+ [Lego sets]!"

Katerina Siniakova is still giving Naomi Osaka plenty to think about as she closes from 40-0 to 40-30, but the two-time champion continues to have too much in the key moments and completes another hold.

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That's a huge hold for Katerina Siniakova.

The Czech is on the back foot throughout her latest service game but saves a break point to recover to deuce, before getting over the line.

That could be massive for her belief - but Naomi Osaka is looking really sharp here.

Mark Woodforde
17-time Grand Slam doubles champion on BBC Radio 5 Sports Extra 2

It's a much more disciplined approach from Iga Swiatek.

I am always curious to watch from the side of the court when I see Swiatek, just to see that spin she puts on the ball.

Katie Smith
Presenter on BBC Radio 5 Sports Extra 2

It's another comprehensive victory from the former champion, Iga Swiatek.