Novak Djokovic says the furnace conditions at the Australian Open were right on the limit as he won a survival of the fittest battle with Gael Monfils to reach the third round on Thursday.
The six-time champion staggered over the finish line to stretch his unbeaten record over Monfils to 15-0, one of the longest at Tour level, after dropping the opening set.
Djokovic, playing in his first tournament for six months after an elbow injury, just did enough at the end to carve out a 4-6, 6-3, 6-1, 6-3 win in 2hr 45min on baking Rod Laver Arena.
The 12-time Grand Slam champion has a day to recover for his third round encounter with Spanish 21st seed Albert Ramos-Vinolas.
Playing conditions were described as brutal as temperatures hovered around 40 Celsius (104 Fahrenheit), prompting Djokovic to say a safety limit had been reached for the players.
"People might say at this level you have to be as a professional tennis player fit," Djokovic said.
"It's the beginning of the season. You work and train hard to be able to sustain these kind of conditions, to be tough.
"But I think there is a limit, and that is a level of tolerance between being fit and being, I think, in danger in terms of health. It was right at the limit."
The extreme elements made it a desperate struggle just to finish the match with Monfils looking the worse for wear early before Djokovic had enough in the tank to win on his fourth match point in a gruelling eight-minute final game.
"It was brutal conditions and we both suffered, it was a big challenge for both of us," Djokovic said.
"Gael is one of the best athletes in our sport but he was not at his best in the second and third sets. It was about just hanging in there and try to use every opportunity."
Monfils, who was often hunched over gasping for air in between points, said it was the hardest match he had played.
"It was tough to breathe. Yeah, I think it was the hardest (match) I have," Monfils said.
"No matter how much you train in the heat, how much you like the heat, it's very tough, maybe a little bit too hot."
Monfils added: "I got super dizzy. I think I had a small heat stroke out there.
"I trained this winter in Miami. Was pretty hot. I thought I was very good. I'm telling you, I was dying on the court for 40 minutes."
Djokovic, showing the effects of the struggle, fended off Monfils' renewed late effort and the Serb needed his fourth match point to claim victory.