Novak Djokovic and Gael Monfils questioned the decision to allow play to continue at the Australian Open as temperatures reached 40 degrees Celsius on Thursday.
The pair put on an exciting display in their second-round match at Melbourne Park, Djokovic getting the better of his French opponent 4-6 6-3 6-1 6-3.
Monfils appeared to struggle more than the six-time champion in the searing heat, his game falling off after an impressive start to allow Djokovic to fight back.
Speaking after his defeat, the world number 39 said the conditions were some of the toughest he had ever played in, labelling them dangerous.
"It was tough," he said. "It was really warm, it was tough to breathe. I think it was the hardest I have [played in].
"I got super dizzy. I think I had a small heat stroke for 40 minutes. I couldn't feel fresh. I tried to cool down, but even with ice towel, the water [I could not].
"I'm telling you, I was dying on the court for 40 minutes. I think sometimes we put our body at risk."
-- Gael Monfils (@Gael_Monfils) January 18, 2018
Djokovic echoed Monfils' concerns, describing his time on the court as "brutal" and called on organisers to take the players into account when planning the schedule.
"The conditions were brutal," said the Serbian. "It was a big challenge for both of us to be on the court, to be able to finish the match.
"I'm just glad that I managed to come out on top."
He added: "I think there are certain days where you just have to, as a tournament supervisor, recognise that you might need to give players a few extra hours until it [the temperature] comes down.
"I think there is a limit. [Today] it was right at the limit."
The Tower of Tandil-- #AusOpen (@AustralianOpen) January 18, 2018
With his wicked fearhand @delpotrojuan outlasts Karen #Khachanov in one of the most intense matches of the tournament so far. The final score 6-4 7-6(4) 6-7(0) 6-4. #AusOpenpic.twitter.com/QCWiIuIySD
It was not only Djokovic and Monfils struggling in the heat, Juan Martin del Potro also had to play in the hottest part of the day, the Argentine beating Karen Kachanov in four sets.
"It was really difficult to play," he told a media conference. "Almost 40 degrees out there is too much for the health.
"We did a big effort to play good tennis, [but] the weather was too high for playing tennis. Also you can see the crowds, nobody was there watching under the sun.
"But I survived. I will play after tomorrow I hope in different conditions."