An extraordinary meltdown from world No.1 Rory McIlroy has left his Australian Open title defence in tatters.

McIlroy had been cruising along in a share of the lead before imploding to leak five shots in the space of two holes midway through his third-round howler on Saturday.

His disastrous triple-bogey seven on the par-4 ninth en route to a five-over 76 was like a scene straight out of Tin Cup.

After blocking his tee shot into waist-high grass, McIlroy briefly lost his mind and his mad gamble to try to muscle the ball out backfired spectacularly.

Looking more like a weekend hacker than four-time major winner, McIlroy chopped the ball into even deeper strife, completely submerging it under flaky matting and being forced to take a penalty for an unplayable lie.

Even with the benefit of two club lengths’ relief, McIlroy still wasn’t out of the rough and could only manage to punch the ball about 100 metres before finally finding the green with his fifth shot.

He was unable to hole his three-metre putt and suddenly plummeted from a share of the lead to three shots off the pace.

But that was only half of it.

On the very next hole, McIlroy dragged his approach into the trees, was unable to find the fairway with his recovery shot before chipping up and missing his bogey putt and walking off with a double-bogey six.

In the twinkle of an eye, the defending champion crashed from four-under-par to one over and six strokes off the lead.

To complete his woes, McIlroy’s threesome, which also two-time champion Greg Chalmers and Adam Crawford, was put on the shot clock by officials for slow play.

He briefly stopped the bleeding with a birdie at the next, but blundered again with a sloppy bogey on the par-4 13th.

After overhitting his approach, McIlroy chipped through the green and needed to hole a two-metre putt to avoid racking up another double.

McIlroy’s round – which also featured a supersonic 330-metre drive on the seventh hole – ended with a birdie at the par-5 last and came after he mixed an eagle with six birdies and six bogeys on Friday.

Incredibly, in his first 54 holes, the Northern Irishman has posted 13 birdies, 28 pars, 11 bogeys, one double and a triple.

Ominously, though, he is not completely out of the tournament, still lurking six strokes off the lead heading into Sunday’s final round.