Novak Djokovic won his fifth Australian Open after rebounding from physical collapse to outlast four-time finalist Andy Murray in an exhausting four-set contest on Sunday.

In a replay of the tournament's 2013 final, both were inseparable until the third set when Djokovic broke ranks and ran away with the championship 7-6 (7-5), 6-7 (4-7), 6-3, 6-0 in three hours and 39 minutes.

"There were a lot of turning points in the match," said the victorious Serb. "Very physical, very exhausting. We both went through some tough moments physically."

The world No.1's eighth Grand Slam was earned the hard way as the pair, who have known each other since childhood, matched each other in every facet.

Long rallies from the baselines - 78 points exceeded eight shots - reigned supreme as each player chose to work the other into a vulnerable position rather than attempt quick winners.

"It was a cat-and-mouse fight," said Djokovic. "It always is. We always try to outplay the opponent with ground strokes, long rallies (and) a lot of variety in the games: spin, flat, slice, drop shots.

"I think we both went out with the full repertoire of shots."

Murray had more than a few opportunities to break clear and clinch his first Australian Open title but crumbled under pressure when each came his way.

The loss follows those at Melbourne Park in 2010, 2011 and 2013 and is the two-time Grand Slam champion's sixth loss in a major final.

In the opening stages of both the second and third sets, Djokovic's left ankle buckled underneath him and the world No.1 dropped to the ground.

He later claimed it was just his energy levels dropping following the excruciating tiebreaker sets.

Regardless, the sight of his competitor wounded played on the mind of Murray who quickly conceded breaks he had only just earned.

In the latter instance, he never recovered and lost 12 of the final 13 games in a capitulation that underplayed the enthralling battle of the opening sets.

"The third set was frustrating because I got a bit distracted when he fell on the ground after a couple of shots," said the Scot.

"It appeared that he was cramping and then I let it distract me a little bit.

"That's what I'm most disappointed about."

Both players exchanged a couple of service breaks in the 72-minute opening set before Djokovic came back from 4-2 down in the tiebreak to win five of the last six points with a mix of aggressive tennis and Murray errors.

Murray bounced back from that disappointment to grab a 2-0 lead in the second - only to forfeit it after Djokovic fell awkwardly on his left ankle.

As both struggled to place a legal first serve, the breaks of serves continued but neither could break free.

A sliver of a chance came Murray's way as Djokovic served at 4-5 but the world No.1 soon saved that set point and pressured the next Murray game.

Murray, ever-muttering to himself, shouted, "Wake up" as Djokovic threatened another service game before the Scot forced another tiebreaker.

He didn't make the mistake of the first set's decider and ensured his 4-2 lead this time round became the 7-4 score to bring the contest back again level.

Having taken more than two-and-a-half-hours to complete just two fierce sets, it seemed the winner would be last man standing.

The battler Djokovic again stumbled, clutching at his left calf and ankle while a weary Murray netted forehands in increasing frequency as his footwork slowed.

But as Djokovic began losing ground physically, he gained many strides in the psychological department as Murray focused on his opponent's afflictions.

The end result: Murray, beside his smashed racquet, watching the world No.1 again bask in the glory of another Australian Open win.

Djokovic's eighth major title takes him to equal-eighth place of all time, alongside Andre Agassi, Ivan Lendl, Jimmy Connors, Fred Perry and Ken Rosewall.