NEW YORK » Roger Federer is one cool customer.

The temperature climbed into the 90s yet again yesterday at Flushing Meadows, and the guy showed up for work wearing a warm-up jacket. Then he put in his 1 hour, 41 minutes on court, dismissing 104th-ranked Andreas Beck of Germany 6-3, 6-4, 6-3 with the help of 15 aces, to ease into the third round of the U.S. Open.

"It’s about just saving your energy for the really big match coming up, maybe the next one," Federer said, perhaps mindful that he was pushed to five sets in the opening round at Wimbledon in June before eventually losing in the quarterfinals at a second consecutive major tournament.

He dropped all of seven games in the first round of the U.S. Open, and the owner of a record 16 Grand Slam titles is feeling pretty good about things at the moment.

"It’s the perfect start, sure. I played Monday; had two days off. I had another easy one physically today, and here I am in the third round feeling like I’m completely in the tournament," said Federer, a five-time U.S. Open champion and the only man left in the field who has won it.

"I got a sense for how the court speed is again. I got the sense of the crowd and the wind now, as well. I played one night, one day," he continued. "I have all the answers after two matches."

In other words: Let everyone else sweat it out.

Like Kei Nishikori, the 147th-ranked qualifier from Japan, who fought cramps in his racket-holding right hand and elsewhere while taking a minute shy of 5 hours to wrap up a 5-7, 7-6 (6), 3-6, 7-6 (3), 6-1 victory over 11th-seeded Marin Cilic.

"It was very humid. It wasn’t easy to get the oxygen," said Cilic, a U.S. Open quarterfinalist last year, and an Australian Open semifinalist in January.

The 20-year-old Nishikori began feeling his muscles tighten in the second set, but didn’t really begin worrying until after trailing 2-1 in sets.

"I was thinking about it in fourth set, mostly: ‘Even if I win this, I have to play one more set. It’s not going to be easy for me, you know, cramping,’ " said Nishikori, who reached the fourth round two years ago, the first Japanese man since 1937 to get that far at the U.S. Open. "But I was able to fight through."

His was one of a handful of upsets on Day 4 of a tournament that is quickly accumulating surprises. Beatrice Capra, an 18-year-old from Ellicott City, Md., made like 2009 U.S. Open darling Melanie Oudin and ousted No. 18-seeded Aravane Rezai of France 7-5, 2-6, 6-3.

No. 9 Agnieszka Radwanska lost to Peng Shuai, and No. 22 Maria Jose Martinez Sanchez lost to Patty Schnyder. Seeded winners included 2004 champion Svetlana Kuznetsova, 2008 runner-up Jelena Jankovic and 2010 Wimbledon finalist Vera Zvonareva. Top-seeded Caroline Wozniacki, like Federer, didn’t waste any time on court, blanking 84th-ranked Chang Kai-chen 6-0, 6-0.