Novak Djokovic placed ice packs around his neck and on top of his head during changeovers to keep cool amid the Paris heat wave at the French Open on Wednesday.
Djokovic, 39, was pushed by 74th-ranked French player Valentin Royer, who is 15 years younger than him, for more than 3½ hours before he reached the third round with a 6-3, 6-2, 6-7 (7), 6-3 victory.
For the fourth straight day of this year's tournament, the temperature rose beyond 90 degrees Fahrenheit.
Along with the heat, Djokovic faced ongoing booing, and he expressed displeasure with the crowd making noise during points and in between serves. When he saved a break point at a crucial moment in the fourth set, Djokovic put his finger to his lips in the direction of the home fans, earning loud jeers.
"It was a very, very difficult match in difficult conditions," Djokovic said. "A big challenge for me. ... Experience helped me a lot."
When Djokovic won a key point early in the fourth set with a forehand that he whipped around the net post from far off the court, the 24-time Grand Slam champion waved his arms toward the crowd inside Court Philippe-Chatrier.
Djokovic wasted a chance to close the match out earlier when he missed a backhand long in the third-set tiebreaker then required four more match points in his final service game before a forehand from Royer finally landed in the net to conclude a long rally.
When it was finally over after 3 hours, 44 minutes, Djokovic first nearly stumbled to the clay then performed his violin celebration.
"It's a very important victory," Djokovic said. "The conditions are difficult for players. I had chances in the third set, and it was my fault because I was twice a break up.
Before arriving in Paris, Royer had earned only one tour-level win across 11 tournaments this season.
Djokovic came to Roland Garros with questions over his form after he lost his only clay-court match before the tournament, falling to Croatian qualifier Dino Prizmic at the Italian Open after two months out due to a right shoulder injury.
But Djokovic is playing himself back into form after coming back from a set down to beat Giovanni Mpetshi Perricard, another Frenchman, in a first-round match that lasted nearly three hours.
Djokovic improved to 14-0 in his career against Frenchmen at Roland Garros and reached the third round in Paris for a 21st straight year. He raised the Coupe des Mousquetaires trophy in 2016, 2021 and 2023.
"Hopefully I won't face another Frenchman until the end of the tournament," Djokovic said with a laugh during his on-court interview. "Oh my god, I've had enough. I've played two matches, and I feel like I've played two weeks."
A pair of Djokovic fans inside the main stadium held up a sign with a goat on it that read "39 is the new 29."
Up next for Djokovic is potentially a bigger test against either 19-year-old Brazilian Joao Fonseca or the 20-year-old Prizmic, who were playing later. Fonseca has been touted as a future Grand Slam contender, while Djokovic himself pointed to big things ahead for Prizmic after their meeting in Rome.
No. 11 Andrey Rublev and No. 13 Karen Khachanov were among those also advancing to the third round Wednesday. Jakub Mensik collapsed to the clay because of cramps and had a tough time getting up after besting Mariano Navone in a fifth-set tiebreaker. The match lasted 4 hours, 41 minutes.
Later, second-seeded Alexander Zverev was playing Tomas Machac in the night session.
The Associated Press and PA contributed to this report.