Title favourite Naomi Osaka survived a scare against Ukrainian teenager Marta Kostyuk to reach the fourth round of the US Open.

The third seed had to save five break points to avoid going 3-1 down in the decider before pulling away to win 6-3 6-7 (4) 6-2.

Osaka once again wore heavy strapping on the left hamstring she injured last week while her mask bore the name of Ahmaud Arbery, a 25-year-old unarmed black man who was shot dead while out running in February.

Osaka has masks with different names on for all seven rounds, and she showed just how much she wants to repeat her triumph of two years ago.

Kostyuk reached the third round of the Australian Open in 2018 aged just 15 but this was her first moment in the limelight since and she certainly rose to the occasion.

Having faced pressure in most of her service games, the now 18-year-old made Osaka pay for missed chances by taking the second set on a tie-break and, had she converted on any of the break points at 2-1 in the third, the result may well have been different.

"I feel like that game was very important, and honestly, I'm not sure how it would have went if she won it and I would have had to break her back, but thankfully I don't have to think about it too much," a relieved Osaka revealed.

"Of course in the third set towards the end I feel like physically I was better, and I was, of course, more experienced. But, yeah, I feel like she's definitely going to be dangerous."

On her injury, she added some positive news: "I felt like I was moving well today.

"It could be better, but I think for a three-set match, the amount of movement that I did, and the fact that I felt like I could have kept going if I really needed to is definitely a good sign."

Fellow former champion Angelique Kerber is also through to the last 16 after a 6-3 6-4 victory over Ann Li, and a fascinating contest awaits against in-form American Jennifer Brady, who knocked out Karolina Pliskova's conqueror Caroline Garcia.

Two-time Wimbledon champion Petra Kvitova made it through to the fourth round after a straight sets win over Jennifer Pegula.

The Czech took out the 26-year-old American 6-4 6-3 to set up a meeting with another home favourite in the shape of Shelby Rogers.

Rogers reached this stage of the US Open for the first time with an easy win over compatriot Madison Brengle.