Former men's singles champions Novak Djokovic and Marin Cilic opened their campaigns for a repeat victory at the US Open with contrasting first-round wins in sweltering heat and humid conditions.
Djokovic looked in real trouble in the steamy conditions against Marton Fucsovics and admitted to feeling sick during the almost three hour encounter but recovered to win 6-3 3-6 6-4 6-0 on Arthur Ashe Stadium.
The reigning Wimbledon champion, who has struggled in similar situations in the past, called for the doctor during the second set and trailed by a break in the third before Hungarian Fucsovics, too, began to wilt.
The heat was so brutal at Flushing Meadows that tournament officials added a 10-minute break between the third and fourth set of the men's best-of-five singles matches.
And both players took advantage of the break before Djokovic made swift work of his opponent on the resumption to set up a second-round clash against American Tennys Sandgren, who eased past Viktor Troicki in straight sets.
Cilic clinched a second-round berth after opponent Marius Copil of Romania retired in the third set trailing the seventh-ranked Croatian 7-5 6-1 1-1.
Cilic, who was champion in 2014, was cruising against Copil, who quit with a left-arm strain, according to a USTA official.
Cilic, who said it was "one of the most brutal days that we had so far this year," told reporters the heat, plus the pressure of the shot clock introduced at the tournament this year, had proved challenging.
"I was just missing some easy balls, making some unforced errors that are not that usual for me," he said, referring to his performance early in the match.
"Conditions definitely were extremely tough and very humid, very hot."