ROGER Federer withstood a Marin Cilic comeback to successfully defend his Australian Open title and win a 20th grand slam crown.

Cilic recovered from two sets to one and a break down to force a fifth set but Federer proved stronger in the end to win 6-2 6-7 (5/7) 6-3 3-6 6-1 and join Novak Djokovic and Roy Emerson in claiming his sixth title in Melbourne.

The 36-year-old, the second oldest man to win a slam title behind Ken Rosewall, moves four clear again of Rafael Nadal in terms of overall titles and is only three behind Serena Williams and four adrift of all-time record holder Margaret Court.

When Cilic lost the first four games in 12 minutes, it looked like the match might be as one-sided as their Wimbledon final last summer, when struggles with blisters reduced the Croatian to tears.

This was the third time Cilic has been in this position having won the US Open in 2014 but the nerves were obvious as he lined up against a man in his 30th slam final.

Controversially, the roof was shut on Rod Laver Arena, with the tournament referee using his discretion to implement the extreme heat policy even though it was an evening match and the temperature was not at the 40C threshold.

The combination of heat and humidity arguably made conditions more brutal than when the temperature was hotter earlier in the tournament and the referee may have had the fate of women's runner-up Simona Halep in mind.

The women's final was played in similar conditions, although not quite as hot, and ESPN showed a picture of Halep in hospital on a drip last night, apparently suffering from dehydration after her gruelling battle with Caroline Wozniacki.

The decision certainly seemed to play into Federer's hands. If the Swiss is great outdoors, he is the master indoors, suffocating opponents with his pace of play.

Cilic certainly looked like he needed space to breathe as he dumped a smash into the bottom of the net to drop serve in the opening game and it got worse from there until he composed himself to hold in the fifth game.

Although the first set was gone, the last couple of games at least allowed the 29-year-old to get a foothold, and it was he who eventually claimed a second set that saw both men have chances.

Cilic looked like he might have missed his opportunity when he netted a weak backhand on set point at 5-4 but he made up for it with a terrific tie-break, his improvement in the match demonstrated by the rock solid smash that clinched it.

He was the better player at the start of the third set, too, but Federer found his level again to take it and looked poised to cruise over the line at 3-1 in the fourth.

However, Federer was struggling to find a first serve and Cilic began to crush the second one with his forehand. The Croatian engineered an unlikely turnaround by winning five straight games to force a decider.

He piled the pressure on at the start of the fifth, overpowering Federer from the baseline, but the 36-year-old held firm to save two break points. And with that Cilic's window of opportunity shut.