New York, New York - Two-time champion Naomi Osaka survived a second-set swoon to beat Katerina Siniakova 6-2, 5-7, 6-1 on Thursday and reach the third round of the US Open.

The Japanese 13th seed looked in total control against her Czech opponent, racing through the first set and to a 4-2 lead in the second without facing a break point.

But as Osaka's unforced errors began to pile up – 20 in the second set compared to four in the first – doubles world number one Siniakova pounced.

Serving for the match at 5-3, Osaka was broken – the fourth straight break of serve in the set, still leaving her up 5- 4.

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But Siniakova kept pressing and broke a clearly frustrated Osaka for a 6-5 lead on the way to forcing a third set.

Osaka regrouped in the decider, riding a quick break to a 3-0 lead and fending off a pair of break points in the fifth game to make it 4-1 before breaking Siniakova one more time.

"The match was definitely really tough," Osaka said.

"I just felt like I had to fight. I definitely had a couple of opportunities in the second set, and I think I was a little too hard on myself," said Osaka, who next faces Belgium's Elise Mertens, a 6-2, 7-6 (7/3) winner over Maria Timofeeva of Uzbekistan.

"I took the bathroom break, tried to regroup," Osaka added. "I just told myself that it's an honor to play on this court."