Czech-mate: Wozniacki knocked out in second round; Federer, Murray advance

NEW YORK – Arthur Ashe Stadium was nearly empty by the time fourth-seeded Caroline Wozniacki of Denmark and Petra Cetkovska of the Czech Republic closed out the final match of day four, a three-hour marathon that lasted more than twice as long as Roger Federer's match before them.

Shortly after midnight, No. 149 Cetkovska completed a remarkable upset, defeating fourth-seed and 2014 runner-up Wozniacki, 6-4, 6-7, 7-6.

When Cetkovska built a 4-1 lead in the second set, the stadium started to clear out. That's when Wozniacki finally seemed to find her game, battling all the way back to force a third set.

Those who stuck around were pulling for the comeback – and they nearly got it. Wozniacki had four match points, but failed to convert. At 12:05a.m., they went to a deciding tiebreak. And there, as in the first set, Cetkovska was lights out. Wozniacki only managed one point in the tiebreak as 30-year-old Cetkovska recorded the biggest win of her career. In five previous U.S. Open appearances, she had never advanced beyond the second round. She returned this year after having major hip surgery last September.

“I said it’s now or never,” Cetkovska said on the court after the win. “I was so happy to be able to come back and to compete, and this happens tonight… it’s amazing for me.”

Wozniacki's early exit leaves only three top-10 seeds in the women's draw.

Earlier on Ashe, No. 2 Federer practically walked into the third round. He defeated Steve Darcis, 6-1, 6-2, 6-1. "It was pretty on the easier side, you know, so I was able to mix it up, was attacking, was also staying back some. I was pretty much all-out attack as much as I could," Federer said after the match.

No. 3 Andy Murray had a more challenging day, as Adrian Mannarino claimed the first two sets of their match. Murray pulled it together for the 5-7, 4-6, 6-1, 6-3, 6-1 comeback win. He said later that he has not been feeling well, that he has been battling a head cold that's going around the locker room.

“I’ve come through many tough matches in my career, and I think that’s why when you are behind like that in the scoreline, when you’ve done it in the past, you have the belief that you can come through and do it again," he said. "That definitely helped me here today.”

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Danielle Elliot is a writer for Yahoo Sports. Find her on Twitter and Facebook.