Six-time champion Novak Djokovic is through to the third round of the Australian Open after outlasting French opponent Gail Monfils in sweltering conditions at Melbourne Park.

Djokovic looked far from his best in the 39-degree heat but was still too good for the enigmatic world No.39, maintaining his perfect record against Monfils with a 4-6 6-3 6-1 6-3 victory.

Read more: Australian Open slammed for extreme heat policy

The Serbian 14th seed needed four match points, screaming in frustration on the third after Monfils hit a cross-court forehand winner to extend the two hours, 45-minute match.

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A visibly drained Monfils had earlier looked close to retiring after taking the first set over a slow-starting Djokovic.

The 193cm baseliner was gasping for air between points and approached the chair umpire midway through the second set to warn that he was on the verge of collapsing.

"Monfils is physically in a daze right now," four-time grand slam winner Jim Courier said on the Seven Network.

"He is hurting badly. A 24-shot rally may have wounded him ... he has got nothing."

France's Gael Monfils bends over while playing Serbia's Novak Djokovic. Photo / AP Photo
France's Gael Monfils bends over while playing Serbia's Novak Djokovic. Photo / AP Photo

Monfils was seen by the tournament doctor and briefly left the court after giving up the second set.

He returned and held serve to start the third set but Djokovic remained in control.

The 12-time grand slam winner began to also feel the heat during the fourth set, appearing to complain to his players' box with coaches Andre Agassi and Radep Stepanek watching on.

But Djokovic, who is coming back from a six-month elbow injury layoff, held on to claim a scrappy victory in which he made 40 unforced errors and sent down 11 double-faults.

He will play Spanish 21st seed Albert Ramos-Vinolas in the round of 32 at Melbourne Park.