Jakub Mensik collapsed on court after his second-round win and Novak Djokovic sweltered for almost four hours as players were made to work hard on another hot Paris day at the French Open.
Temperatures reached the mid-30s in Celsius as the heatwave in France continued.
Czech Mensik was overcome with emotion and cramp as he fell to the floor after beating Argentina's Mariano Navone 6-3 2-6 6-4 1-6 7-6 (13-11) in four hours and 40 minutes.
Mensik - whose flashes of brilliance in his young career have been beset by injury - was struggling to move and needed eight match points to close out victory.
After he fell the floor, opponent Navone crossed the net to congratulate him and also help him up, but Mensik was unable to move.
The 26th seed lay on the floor for several minutes and was attended to by a number of medical staff, who placed ice packs on his head, neck and chest to help.
An ice pack was also laid on the floor for Mensik to rest his head on like a pillow.
Eventually, Mensik was helped to his feet and was able to walk off court, only to struggle again again as he headed towards the locker room.
The 20-year-old was then placed in a wheelchair and taken away - it remains to be seen if he will recover for his third-round match against eighth seed Alex de Minaur on Friday.
Mensik was competing on one of the outer courts at Roland Garros, which offer no shade.
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Djokovic faced home hope Valentin Royer on Court Philippe Chatrier, which has a roof, but he too was exposed to the blazing sun.
The Serb lost a tight third set on a tie-break but regrouped brilliantly to win 6-3 6-2 6-7 (7-9) 6-3.
"He's 39 years of age and is breathing quite hard at the end of this match," former British number one Greg Rusedski said on BBC Radio 5 Sports Extra.
"This was a true test for Novak. He's going to have to up his level again if he's going to continue."
On Monday, Casper Ruud said he felt he was "walking around like a zombie" and feared he had heat stroke after struggling with cramping in 33C temperatures.
French Open organisers monitor the temperature through two wet bulb sensors - one on Court Philippe Chatrier and one on Court 14.
If the threshold is reached, a 10-minute break may be introduced after the second set of women's matches and the third set of men's matches.
If temperatures continue to rise, matches can be suspended until the heat drops.
No French Open match has ever been halted because of extreme heat.
