NEW YORK — Roger Federer might not be so keen to try out his old-dog-new-trick, rush-the-net “SABR” – “sneak attack by Roger” – return strategy against his next opponent at the U.S. Open.

“I don’t think so,” Federer said. “I can always try. But it’s probably not the right guy to do it against.”

Probably not.

That’s because the second-seeded Federer, who advanced Saturday by beating 29th-seeded Philipp Kohlschreiber of Germany 6-3, 6-4, 6-4, will have to deal with 6-foot-10 American John Isner and his massive serve in the fourth round.

“The idea is not to use it very much against a player like that,” Federer said about his innovative and risky approach to attacking second serves, racing forward as the ball arrives to pluck it off the ground with what amounts to a half-volley. “I have done pretty well over the years against big servers, so, I mean, clearly I will think about it. But I don’t think that’s going to be the turning point of the match, to be quite honest. I need to make sure I protect my own serve first.”

Federer has been doing that rather well lately. While dropping a total of only 20 games and zero sets through three matches, he has been broken only twice – both times by Kohlschreiber.

Of Federer’s 17 Grand Slam titles, five came at Flushing Meadows from 2005-08, and he has reached the fourth round for the 15th year in a row.

The 13th-seeded Isner, meanwhile, had lost in the third round each of the past three years – and each time, coincidentally, against Kohlschreiber.

After moving on when Jiri Vesely of the Czech Republic retired because of a neck injury after dropping the first two sets, Isner was asked about the possibility of dealing with Federer’s newfangled return on Monday.

“I haven’t thought about that too much, actually,” said Isner, who is 1-4 against Federer, including losses at the 2007 U.S. Open and, most recently, the 2012 London Olympics. “So I have probably … I don’t know, 48 hours to think about that.”

Vesely is the 16th player – 14 men, two women – to stop during a match at this year’s U.S. Open because of injury or illness, a record for a major tournament in the Open era, which began in 1968.

Isner is one of two U.S. men left, because 68th-ranked Donald Young came all the way back to eliminate 22nd-seeded Viktor Troicki of Serbia 4-6, 0-6, 7-6 (3), 6-2, 6-4. Young had never won a match after losing the first two sets until Tuesday, when he did it against 11th-seeded Gilles Simon in the first round.

“It was 90 percent you guys,” Young told the spectators, “10 percent me.”

Three past major champions in the women’s draw won Saturday afternoon – No. 5 Petra Kvitova, No. 20 Victoria Azarenka No. 22 Sam Stosur. No. 2 Simona Halep, the 2014 French Open runner-up, beat Shelby Rogers of the U.S. in a night match.

Twice the title winner at the Australian Open and twice beaten by Serena Williams in the U.S. Open final, Azarenka needed six match points and nearly three hours to close out 11th-seeded Angelique Kerber 7-5, 2-6, 6-4.

Afterward, Azarenka said she told herself, “I’m going to stay here all day,” if that’s what it was going to take to win.

Federer, meanwhile, has been taking advantage of the brevity of his matches, spending the free time with his wife and their two sets of twins or playing tourist in New York.