With conditions hot and muggy during the afternoon matches at the U.S. Open, David Ferrer and Gilles Simon were tested in a four-set duel. Simon outlasted Ferrer, the No. 4 seed, 6-3, 3-6, 6-1, 6-3, on Sunday to reach the fourth round.

“I feel it was one of the hardest days for me on the court because it was hot and it was so humid,” Simon said. “I never sweat like this in the last 10 years, I feel. So it was really difficult. . . . I mean, it’s not very often that him and me are tired like this just after two hours.”

Ferrer had 11 break points but won just three, while the 26th-seeded Simon won seven of nine. Ferrer’s clothes were so drenched with sweat that he changed his shirt and his shorts midway through the match.

“I was not good with my fitness,” Ferrer said. “He was better.”

Simon said he wasn’t prepared for the 90-degree temperatures and humidity because he had heard it was supposed to be a cooler day with rain. The rain and lightning came later, suspending matches at 4:30 p.m, including Roger Federer’s. Play eventually resumed and Federer beat Marcel Granollers, 4-6, 6-1, 6-1, 6-1.

‘Relaxed’ Tiafoe is settling in

Francis Tiafoe is feeling more comfortable at the U.S. Open than he has at any other Grand Slam juniors tournament this year. Tiafoe, a Riverdale Park native, reached the second round with a 6-2, 6-3 win over Chan-yeong Oh.

“I love the Open,” said Tiafoe, 16. “It’s my favorite slam. The atmosphere is pretty darn good. Everyone is going wild, especially for the Americans. I just feel at home, and I feel relaxed here. I’ve played my best here.”

Tiafoe played in the men’s doubles main draw with fellow 16-year-old Michael Mmoh, losing in the second round. Being here an extra week gave him an opportunity to hit with John Isner, the highest-ranked American. He said playing in doubles gave him confidence for the junior tournament.

“I’ve been playing pretty well the last couple of weeks,” said Tiafoe, the tournament’s No. 6 seed. “I’m just hoping to hopefully go for a run here.”