– His cheeks red, hair matted with sweat, Novak Djokovic appeared to be in such distress as he trudged to a changeover on a steamy U.S. Open afternoon that someone suggested it would be a good idea to have a trash can at the ready, just in case he lost his lunch.

Djokovic sat down and removed his shirt. He guzzled water from a plastic bottle. He placed one cold towel around his neck, a second across his lap and a third between his bare upper back and the seat.

He was not even 1 hours into his first match at Flushing Meadows in two years, and while Djokovic eventually would get past Marton Fucsovics 6-3, 3-6, 6-4, 6-0 Tuesday, it was a bit of an ordeal.

"Survival mode," Djokovic called it.

With the temperature topping 95 degrees and the humidity approaching 50 percent — and that combination making it feel more like 105 — nearly everything became a struggle for every player across the grounds on Day 2 of the U.S. Open, so much so that no fewer than six quit their matches, with at least four citing cramps or heat exhaustion.

About 2 hours into the day's schedule, the U.S. Tennis Association decided to do something it never had at this tournament: offer men the chance to take a 10-minute break before the fourth set if a match went that far. That is similar to the existing rule for women, which allows for 10 minutes of rest before a third set when there is excessive heat.

How bad was it out there at its worst Tuesday?

"Bloody hot," said two-time major semifinalist Johanna Konta, who lost 6-2, 6-2 to No. 6 Caroline Garcia. "Brutal," said 2014 U.S. Open champion Marin Cilic, who advanced when his opponent retired in the third set.

"Really not easy," said three-time Grand Slam title winner Angelique Kerber, who defeated Margarita Gasparyan 7-6 (5), 6-3.

Roger Federer, however, looked cool as he improved to 18-0 in first-round matches at the U.S. Open with a 6-2, 6-2, 6-4 victory over 117th-ranked Yoshihito Nishioka in a night match.