For Caroline Wozniacki, it was like "drinking a margarita on a beach" but for Argentina's Leonardo Mayer it felt "like I was going to die" as temperatures nudged towards the 40-degree mark at the US Open on Tuesday.
Four of eight early men's first round matches ended in retirements. Temperatures were soaring to 38 degrees (100 farenheit) by mid-afternoon, the effect made worse by suffocating humidity.
That may be short of the 41 degrees which remains New York's record temperature in 1936 but it was little consolation to Argentine veteran Mayer who was 6-4, 6-4, 4-6, 2-1 down to Serbia's Laslo Djere when he quit.
"I had heat stroke. I was not going to die on the court, tennis is not for that," said the 31-year-old.
"In the locker room I saw several people lying there, just like me, it's very hard. I could not do it anymore."
Italian qualifier Stefano Travaglia retired at 6-2, 2-6, 7-6 (8/6), 3-0 down to Hubert Hurkacz of Poland and said his cramping was a result of the heat.
"It was 36, 37 degrees but on court it was more," said the 26-year-old who admitted "the first problem was the sun".
"To have 25 seconds between points in this weather is not possible.
"There was a lot of humidity, it was really tough. I hope that in my next tournament it will be less hot."
Ricardas Berankis retired against Chung Hyeon due to heat while Marius Copil's pull-out against 2014 champion Marin Cilic was attributed to an arm injury.
French player Alize Cornet described the conditions as a "nightmare" as she slumped to a three-set loss to Johanna Larsson of Sweden.
Cornet, 28, wept as she sat courtside, telling doctors that she was ready to vomit and felt pain in her head and bones.
Cornet had already been hit with a code violation for changing her shirt on the court after putting it on the wrong way round during the "heat rule" break allowed by the WTA after two sets when the temperature goes beyond 30.1 degrees.
In response to the conditions, tournament organisers have allowed the men to opt for a similar 10-minute off-court rest at two sets to one.
"The tournament referee, along with the medical team, will continue to monitor on-site conditions, to determine when the Extreme Heat Policy will no longer be in effect," said a statement.
US Open press chief Chris Widmaier said that this year is the first time the men's tournament has benefitted from a heat rule which will be reviewed on a day-to-day basis.
However, he ruled out closing the roofs on the showpiece Arthur Ashe and Louis Armstrong courts as that measure is for rain only.
Australian Open champion and second seed Wozniacki dreamed her heat troubles away as she defeated 2011 champion Samantha Stosur 6-3, 6-2 on a sweltering Arthur Ashe Stadium.
"I just tried to cool down between games, used ice. I'm just thinking I'm on the beach, I have a margarita in hand, life is good," she said.
Two-time Wimbledon champion Petra Kvitova was just happy to finish her 6-4, 6-1 win over Yanina Wickmayer before the afternoon began to really cook.
- 'Horrible' heat -
"I was pretty lucky to play first on today, definitely. I knew it's going to be very hot, but I couldn't imagine how horrible the heat was," said the Czech.
Japan's Naomi Osaka couldn't understand what all the fuss was about.
"With this heat, everyone was complaining about it. So I thought it was pretty decent, like, Florida summers are way worse, I think," she said after beating Laura Siegemund of Germany 6-3, 6-2.
The heat and humidity had already been an issue on Monday when Stan Wawrinka, Kevin Anderson and David Ferrer all needed medical time outs.
Ferrer quit his match against Rafael Nadal while Canadian teenager Félix Auger-Aliassime retired facing compatriot Denis Shapovalov after a worrying increase in his heart rate.
"That wasn't easy to see," said Shapovalov. "It's tough to keep pounding at it when he's a brother to me."
In total on Monday, there were four retirements. The record for a first round was 12 in 2015.
The United States national weather service says its heat advisory for New York City will remain in place until Wednesday night.
"The combination of hot temperatures and high humidity will combine to create a situation in which heat illnesses are possible," said the body.