-- NEW YORK -- Jack Sock, a 22-year-old American, is the latest victim of the heat wave that has gripped the 2015 US Open.
In a dramatic moment that shook the overflow Grandstand crowd, Sock collapsed on the court Thursday afternoon early in the fourth set of his second-round match with Ruben Bemelmans. Sock was carried out of the stadium by trainers and security as fans gave him a standing ovation.
"Playing in the US Open is the biggest and most important moment of the season for me, so having to retire from my match today is extremely disappointing," Sock said in a statement. "I want to thank everyone for their support and can't wait to be back next year. I feel better already and look forward to playing Davis Cup."
Less than two hours after his match ended, Sock was spotted in the players' facility. Red-faced and sipping a cup of ice water, Sock limped around in small circles in the atrium leading to the players' garden.
The tournament saw a first-round Grand Slam record of 10 retirements, most of them heat-related. Ice towels have been a popular item with players as they sit in their changeover chairs.
The 12 retirements by men's players at this US Open are also an Open-era record for any Grand Slam.
Sock won the first two sets comfortably, 6-4, 6-4, but Bemelmans began serving better and forced a fourth set. With Bemelmans leading 2-1, Sock -- who had been visibly cramping beforehand -- went down. Witnesses said his eyes rolled back in his head.
"I gave it my all, kept on fighting to the end," Bemelmans said afterward. "Too bad he was cramping. I know the feeling. I cramped in Davis Cup. It's not a good feeling."
The recorded temperature exceeded 90 degrees with 40 percent humidity.
"Bad, very bad," said John Isner of Sock's forced retirement. "When I warmed up at 11:30, it was already pretty toasty."
"We've been here in North America for some time. It's not like, all of a sudden, hot," Federer said. "I mean, it was more on the warmer side, but it's not like impossible, to be quite honest.
"Really no excuse for that. I think everybody should be well-prepared."
Federer added he believes improved conditioning would alleviate some of the problems players are having.
"I think other players should be so fit that heat really shouldn't matter at that point, the ones we've been playing in," Federer said.
The WTA's extreme weather policy was invoked at 1 p.m. ET Thursday when the temperature climbed past 86.2 degrees Fahrenheit. This meant that women could ask for a 10-minute break between the second and third sets if they wished.
The USTA and the other three Grand Slams employ the WTA rule for women's matches.
Conversely, the ATP has no such rule, despite the fact that men play best-of-five-set matches, as opposed to best-of-three for women. Only two of the retirements have been by women at the US Open.
The ATP said in a statement that it has discussed implementing a heat rule but that "there has not been sufficient support or consensus for a specific heat rule to be introduced at ATP events, where matches are best-of-three sets and frequently scheduled later in the day at tournaments that are prone to extreme heat weather conditions.
"Nonetheless, the ATP medical services team does exercise a number of protocols when necessary in the case of extreme heat on the Tour."
The Australian Open, where temperatures can soar into the 100s, is the only Grand Slam with its own heat policy, which takes into consideration several atmospheric conditions and gives the tournament the power to suspend matches.
On July 1, Wimbledon experienced the hottest day, 96.2 degrees Fahrenheit, in its 138-year history. More than 170 people were treated that day, and five were sent to the hospital.
American Mardy Fish did not withdraw Wednesday, but he suffered severe leg cramps before limping through a grueling five-set loss in the final match of his career.