Monfils took the first set but began to suffer in the second, complaining of feeling dizzy and leaving the court with a doctor.
'No matter how much you train in the heat, how much you like the heat, is very tough.
The extreme elements made it a survival of the fittest 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.
"When you can see the impacts (of the weather) on a person are as acute as they are that's when you need to look at this more subjectively and respond in a humane fashion", Dr Bowen told news.com.au.
But defending Australian Open champion Roger Federer was circumspect on Thursday night saying the heat is part and parcel of the Australian Open and believes organisers are doing their best to put player welfare before profits.
"(Today) was right at the limit". "I'm exhausted and dizzy".
The temperature on the court was well above 40 degrees Celsius and they battled for 2 hours and 45 minutes before Novak converted his 4th match point to book his place in the 3rd round. "I knew she was going to give me a lot of pressure, at 5-4 I thought I'd keep hanging there and try and take my spot", said Hsieh, who was ranked number one in doubles for five weeks in 2014.
Dr Kathryn Bowen, a senior research fellow at the Australian National University (ANU) specialising in climate and health, was watching the match and said common sense should have prevailed, at least closing the roof to shield the players somewhat from the heat.
"People might say at this level you have to be as a professional tennis player fit. but I think there is a limit and there's a level of tolerance between being fit and being in danger in terms of health".
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Gael Monfils nearly collapsed in the second set. "I'm not so sure about that, to be honest", he said.
The 14th seeded Serb will play Spain's Albert Ramos-Vinolas in the third round. You're always obliged to play the mandatory events.
Muguruza said her feet were suffering in the heat as temperatures soared above 39.
The Frenchman returned to Rod Laver Arena but could not stop Djokovic coming through 4-6 6-3 6-1 6-3.
"At times I don't like that". "So I feel like I transported myself into the TV this year and I'm finding myself on Rod Laver Arena competing".
Top seed Simona Halep eased fears over her fitness with a brisk 6-2, 6-2 victory over Canada's Eugenie Bouchard to reach the third round.
Dark horse David Goffin's Australian Open hopes went up in smoke as he fell to a 1-6 7-6 (7-5) 6-1 7- 6 (7-4) to French veteran Julien Benneteau while Juan Martin del Potro fired 60 winners on his way to a 6-4 7-6 (7-4) 6-7 (0-7) 6-4 victory over young Russian Karen Khachanov.
"I didn't expect to play this kind of match, I prefer to watch on TV", joked the 29-year-old, a twice quarter-finalist in Melbourne, during his post-match interview on court.