Five-time champion Roger Federer and 2012 winner Andy Murray reached the US Open second round on Tuesday as the crushing heat took the number of first-round retirements to a record 10.
Second-seeded Federer had little trouble in seeing off Argentina's world number 34 Leonardo Mayer 6-1, 6-2, 6-2 in just 77 minutes on Arthur Ashe Stadium.
The 34-year-old Swiss, bidding to become the oldest champion in New York in 45 years, fired 12 aces, 29 winners and broke serve six times.
"I feel good now. I actually wasn't so confident yesterday. I just felt like maybe it could be one of those matches I just couldn't see coming," said Federer.
The 17-time Grand Slam champion goes on to face Belgium's Steve Darcis, who was handed a place in the next stage when Cypriot veteran Marcos Baghdatis retired injured with a groin strain.
It was the 10th retirement in the men's event in the first round; there have also been two pullouts in the women's draw.
Third seed Murray downed the sport's latest bogeyman, Nick Kyrgios, 7-5, 6-3, 4-6, 6-1 for his fourth win in four meetings against the Australian and third in three Grand Slam matchups this year.
The British star, who has made at least the quarter-finals in New York every year since 2010, goes on to tackle France's Adrian Mannarino.
Kyrgios, the world 37, goes away to contemplate facing Murray again in the Davis Cup semi-finals later this month.
"It was tough, very humid, I had to do a lot of running and defending," said Murray after his night match.
Kyrgios came into the tournament under the shadow of a suspension after his now infamous and lurid Montreal rant at Stan Wawrinka, but that threat only applies to ATP events.
So it was no surprise that the first profanity from the Australian came after just four games of the first set, when he complained about fans taking their seats during points.
Kyrgios, 20, showed glimpses of his undoubted talent but his lack of focus once again cost him and he picked up a warning for swearing as the tie drifted away from him.
His Davis Cup teammate, Thanasi Kokkinakis, was also knocked out, retiring on one leg in the fifth set against French 12th seed Richard Gasquet.
The 19-year-old Kokkinakis, who was caught up in Kyrgios's infamous slur against Wawrinka, suffered severe cramping.
But he battled on, serving underhand and forced to play at walking pace before he finally gave up, losing 4-6, 6-1, 4-6, 6-3, 2-0 after almost three hours in 30-degree heat.
After six men retired on Monday, Kokkinakis, Baghdatis, Ernests Gulbis and Kazakhstan's Aleksandr Nedovyesov joined the walking wounded on Tuesday.
"It's just frustrating because I started playing good tennis. I was getting fired up," said Kokkinakis.
"I went up to hit a swing and volley or something, and both my calves...it was just a disaster."
Nedovyesov was down 6-0, 7-6 (7/2), 1-0 to former champion Lleyton Hewitt when he called a halt after suffering a right shoulder injury.
Hewitt, playing in his final US Open, will take on compatriot Bernard Tomic for a place in the last 32.
Tomic, seeded 24, beat Bosnia's Damir Dzumhur 5-7, 7-6 (7/4), 6-4, 6-3.
Wawrinka, the fifth seed and a semi-finalist in 2013, made the next round with a 7-5, 6-4, 7-6 (8/6) win over Spain's Albert Ramos-Vinoles.
French Open champion Wawrinka will next tackle South Korean teenager Chung Hyeon.
"For sure it's surprising to see so many players pull out," said Wawrinka.
"It was hot today when I practiced at 4. You need to be ready physically for that."
Japan may have lost fourth seed Kei Nishikori on Monday, but 19-year-old Yoshihito Nishioka restored some national pride with a 6-4, 2-6, 6-7 (7/9), 6-1, 6-2 win over fellow qualifier Paul-Henri Mathieu of France.
In the women's draw, Lucie Safarova joined the seeds casualty list when the Czech left-hander became the fourth top-10 player to lose in the first round.
Sixth-seeded Safarova slipped to a 6-4, 6-1 defeat to Ukraine's Lesia Tsurenko, the woman she beat in the semi-finals in New Haven just last week.
Safarova joins seventh seed Ana Ivanovic, eighth-ranked Karolina Pliskova and Carla Suarez Navarro, the 10th seed, in failing to get out of the first round.
World number two Simona Halep avoided the upsets when New Zealand opponent Marina Erakovic retired with a knee injury.
Halep was leading 6-2, 3-0 when her 99th-ranked rival called it quits.
Aussie Samantha Stosur, whose 2011 US Open final win over Serena Williams was the last time the US world number one lost at Flushing Meadows, beat Timea Babos of Hungary 6-3, 6-4.
Two-time Wimbledon winner Petra Kvitova, the fifth seed, needed just 59 minutes to beat German qualifier Laura Siegemund 6-1, 6-1.