A fatigued Novak Djokovic stared down a ferocious challenge from Rafa Nadal to retain his Australian Open title on Sunday in the longest Grand Slam final played.

- Djokovic wins Australian Open

The Serbian World No. 1, who defeated Spaniard Nadal for the Wimbledon and US Open crowns last year, captured the decisive break at 5-5 in the fifth and in a frenzied atmosphere at Rod Laver Arena served out the match to win 5-7, 6-4, 6-2, 6-7, 7-5.

Crossing himself and muttering prayers, Djokovic slammed a cross-court forehand winner on the first match point and collapsed to the ground in ecstasy after the five-hour 53 minute tussle.

He then tore his t-shirt in two before ripping it off and tossing it over his head, roaring at the crowd like a man possessed, to celebrate his fifth grand slam triumph.

"Rafa you are one of the best players ever. One of the most respected players on tour," the 24-year-old Serb said, struggling to hold the Norman Brookes Challenge Cup aloft.

"We made history tonight. Unfortuantely there could not be two winners and I wish you all the best for the season. I hope we will have many more matches and finals."

Djokovic apologised to the crowd after the match which started before 8 p.m. local time on muggy Sunday evening and finished at 1:37 a.m.

The length of the match smashed the previous record for a grand slam final of four hours and 54 minutes set when Mats Wilander defeated Ivan Lendl for the 1988 US Open title.

The win gave top seed and 2008 champion Djokovic his third consecutive Grand Slam title, and he has now beaten Nadal in seven straight finals.

"Congratulations to Novak and his team. They deserve it," said the second-seeded Spaniard, who broke to lead 4-2 in the fifth set but ultimately fell to a more determined opponent.

"They are doing something fantastic, so congratulations ... Every year is tougher and for it to be the first tournament of the year to make the final and play a fantastic match against Novak, thank you very much."

An 80-minute opening set set the tone for the long and gruelling arm wrestle to come. Nadal broke at 5-5 and drew first blood on his third set point when a backhand return floated long.

Steely-eyed Djokovic, wearing black and exuding menace, shrugged off the setback and broke Nadal in the fourth game of the second set.

Dictating the play and attacking Nadal's serve with abandon, the Serbian brought up set points at 5-3, but flinched after Nadal saved them, surrendering his serve with a double-fault.

Nadal was unable to make the Serb pay, however, and with his serves fired back at him, nervously double-faulted to allow Djokovic to level the match.

The Serbian threw an icy glance at his players box before going on to find his range with devastating effect in the third set.

Nadal, whose topspin bombs too often fell harmlessly short, looked rattled as Djokovic motored to a 5-2 lead before closing out the set to love, having lost only two points on serve.

Nadal hung in doggedly, but the Serbian sought a quick kill when leading 4-3 in the fourth, and came within a point of serving out the match after raising three break points.

Under huge pressure, the determined Spaniard saved them all.

Celebrating wildly with a flurry of fist-pumps, Nadal's momentum was stolen when the clouds that had hovered threateningly above the whole match opened and forced a 10-minute delay to allow the stadium's retractable roof to close.

With chants of "Rafa! Rafa!" ringing out from the stands, the inspired Spaniard pulled Djokovic into a tiebreak.

With tension rising to boiling point, ice-man Djokovic lost his cool, and moving in to pick off an easy short ball, smacked his forehand into the net cord when two points away from sealing the trophy and surrendered the set by belting a forehand wide.

Nadal, riding a huge wave of emotion, broke Djokovic to lead 4-2 in the decider, but the gritty Serb broke back immediately and withstood a series of fierce baseline skirmishes to keep pace with the Spaniard.

Grimacing and panting, Djokovic stunned Nadal by raising his game to another level, and his opponent crumbled, slicing a backhand into the net to be broken at 5-5.

Another twist was to come, as Djokovic, two points from victory slammed a simple overhead smash into the net to allow Nadal a final break point.

But the chance went begging and the ice-veined Serb unleashed a booming serve that set up the final winner to maintain his dominance of the Spaniard and the men's game.