NEW YORK -- Roger Federer says his favorite drinks are cold water and a sparkling glass of champagne. Both could be on tap at the US Open: Federer needed a few swigs of water on another steamy day at the Open, and he played like a former champion set to uncork a celebratory bottle of bubbly.
"I don't like warm drinks, let's put it that way," Federer said, laughing.
Federer's coolness on the court belied another day where players needed cooling towels as much as their rackets. Federer, a five-time U.S. Open champion, had steeled himself for the heat by changing up his routine -- he made an early trip to New York to prep his game in the sweltering sun.
"I felt like it's maybe one of these years where it could be hot," Federer said Thursday. "I had the plan to go to Dubai first, where it's extremely hot. I didn't want to be away from the family. I changed plans and said, 'Let's go early to America and prepare over here in the conditions that I'm actually going to see during the Open.'"
Federer was crisp in a 7-5, 6-4, 6-4 win over Benoit Paire and made it 18 of 18 lifetime in the second round of the U.S. Open. Up next, Federer plays No. 30 seed Nick Kyrgios on Saturday.
"Not a bad performance by any means by me," Federer said.
Federer has eased up on his schedule, saying he no longer wanted to just "play, play, play." But when he does, there are still few better on the hard court. And his plan to pass on Dubai -- where temps this week hit 110 degrees -- for the breezy 90s in New York could be a factor in how far he goes.
"If you train in the cold all the time, all of a sudden it hits you, the humidity and heat," he said. "You're just not ready. I don't care how fit you are, what you're used to, the humidity can really get to you. I think that was a good choice."
In other second-round matches, No. 6 seed Novak Djokovic wasted a match point in the third set, before going on to win 6-1, 6-3, 6-7 (2), 6-2 against Tennys Sandgren.
Djokovic had a much easier victory over Sandgren, an American ranked 61st, in Wimbledon's first round this year, dropping only six games in all.
The 13-time major champion seemed to be along the same path at Flushing Meadows on Thursday night, standing one point from victory while leading 5-4 in the third set as Sandgren served at 30-40. But Sandgren ended an 11-stroke exchange with a forehand winner, then took the ensuing tiebreaker.
Djokovic regained the upper hand with an early break in the fourth and was on his way.
No. 4 seed Alexander Zverev, who had been knocked out in the second round in his three previous appearances here, reached the third round with a 6-4, 6-4, 6-2 win over Nicolas Mahut.
The German leads the ATP Tour in wins this year, has already won three ATP Masters 1000 titles and at 21 is the popular pick as the young star most likely to have a Grand Slam breakthrough and end the stranglehold veterans such as Federer, Rafael Nadal and Novak Djokovic have had on the majors.
Zverev -- perhaps benefiting from a tame early draw that started with two lucky losers -- hasn't dropped more than four games in a set so far.
Gael Monfils and Pablo Carreno Busta both retired from their second-round matches because of injuries.
Monfils retired in the second set of his match against 2014 runner-up Kei Nishikori because of an injured right wrist. The 39th-ranked Monfils, a semifinalist at Flushing Meadows two years ago, was treated by a trainer and had his wrist taped up. But he unraveled the tape shortly before saying he could not continue.
Monfils was trailing 6-2, 5-4 when he stopped.
Carreno Busta, who reached the semifinals last year in Flushing Meadows, was unable to duplicate his run, forced to retire from his match because of left thigh pain.
Joao Sousa of Portugal led Carreno Busta 4-6, 6-3, 5-7, 6-2, 2-0 when the No. 12 seed from Spain had to stop playing.
No. 14 seed Fabio Fognini of Italy was upset in the second round by 55th-ranked John Millman of Australia 6-1, 4-6, 6-4, 6-1.
By reaching the third round, Millman equaled his best showing at any Grand Slam tournament.
Fognini, the husband of 2015 US Open champion Flavia Pennetta, was kicked out of the US Open doubles tournament last year after vulgarly insulting a female chair umpire during a first-round loss in singles.
The Associated Press contributed to this report.