Simona Halep and Stan Wawrinka beat the heat with straight-sets wins to reach the third round of a sweltering US Open on Thursday while American hope Jack Sock wilted under the punishing conditions, collapsing on court.
After the sun set on Flushing Meadows, fourth seed Caroline Wozniacki played in cooler conditions but was unable to repel a red-hot Petra Cetkovska, the 149th ranked Czech repeating her 2013 Wimbledon upset of the Dane with a 6-4, 5-7, 7-6(1) win.
Cetkovska had looked to be cruising to victory when she led 4-1 in the second set but the injury-prone 30-year-old lost her way and then saved four match points in the decider before she was ultimately rewarded for being aggressive on vital points.
Leading off the night session, second seed Roger Federer was neither troubled by the weather nor his opponent as the Swiss maestro easily dispatched Steve Darcis of Belgium 6-1, 6-2, 6-1 in just 80 minutes to stay on course for a sixth US Open crown.
While Federer barely broke a sweat, players spent most a sizzling day session with ice packs draped over their shoulders, chugging on water bottles and searching for shade.
British hopes Andy Murray and Johanna Konta, however, enjoyed a productive day in the sun as both went the distance to score second round victories.
Third seed Murray appeared frozen to the spot on a broiling afternoon but caught fire when he needed to and rallied for a 5-7, 4-6, 6-1, 6-3, 6-1 win over Frenchman Adrian Mannarino.
Konta, meanwhile, provided the early upset, toiling for three hours and 27 minutes to see off ninth-seeded Spaniard and Wimbledon finalist Garbine Muguruza 7-6(4), 6-7(4), 6-2 in what was the longest women's match ever at the US Open.
"I noticed after the first set -- it was incredibly long, but then after I had a couple glances on the clock, I'm like, 'Oh, okay. We have been here for a while.' But we deal with it as best we can," said Konta. "It was the same for her and the same for a lot of players playing out there at this time."
As courtside temperatures pushed past 100 degrees Fahrenheit (38 degrees Celsius) at Arthur Ashe Stadium, Romanian second seed Halep wasted little time finishing off Ukraine qualifier Kateryna Bondarenko 6-3, 6-4 in 76 minutes before escaping to the air-conditioned comfort of the players' lounge.
Fifth-seeded Swiss Wawrinka outslugged promising South Korean teenager Chung Hyeon, but still needed three tiebreaks to sweat out a 7-6(2), 7-6(4), 7-6(6) second round decision.
"Today was a really tough day with the conditions," Wawrinka said. "I know that I'm ready physically to battle for long hours in that condition. Today was hot, was humid, but still we play three hours and I'm feeling OK."
Next up for the French Open champion is Ruben Bemelmans of Belgium, who advanced when Sock retired due to cramping while leading 6-4, 6-4, 3-6, 1-2.
Sock had looked in control of the match but began to show signs of distress in the third set, then sent shockwaves through the crowd when he began to cramp and dropped to the court as medical staff rushed to his aid.
A wheelchair was brought out but after several minutes, Sock was helped to his feet and, assisted by a trainer under each arm, limped off the court.
Australian Sam Stosur, the 2011 US Open champion and last player to beat world number one Serena Williams at Flushing Meadows four years ago, looked ready to make another run at the title as she crushed Russian qualifier Evgeniya Rodina 6-1, 6-1.
But it was the end of the road for 2001 champion Lleyton Hewitt, the tenacious Australian dragged kicking and screaming to the Flushing Meadows exit by countryman Bernard Tomic in what was his final US Open.
A player who constructed a career around a relentless fighting spirit that became his calling card, Hewitt was never going to leave the US Open without a struggle and went down swinging until the very end, falling 6-3, 6-2, 3-6, 5-7, 7-5.