Sleep-deprived Lleyton Hewitt has refused to blame controversial scheduling for his latest Australian Open demise after slumping to a disappointing straight-sets loss to Novak Djokovic.

Forced to back up from his sapping 4.34am finish Sunday, Hewitt was unable to repeat his third-round heroics and crashed to a 7-5 6-3 6-3 defeat at the hands of Serbia's fast-rising world No.3.

It was lights out early for Hewitt, who was on court for less than two-and-a-half hours.

But Australia's former world No.1 copped his loss sweet, conceding his farcically late-starting clash with Marcos Baghdatis - which began at 11 minutes before midnight on Saturday - had hardly been a factor.

"I felt ready when I had to go on the court," Hewitt said.

"I started pretty well. As the match went on, maybe I lost that sharpness a little bit, I was ready to go (at) 7.30 tonight when we went out to play."

Asked directly if being involved in the latest-finishing match in grand slam history was to blame for his fourth-round exit, a diplomatic and sporting Hewitt insisted "No, absolutely not. He was too good tonight."

Facing a quick turnaround with his body clock all out of whack, Hewitt returned to Rod Laver Arena with concerns about his ability to recover from his epic four-and-three-quarter-hour battle with Baghdatis as debate continued to rage over whether or not Open officials should have even sent him on court at a ridiculous 11.49pm Saturday.

It was actually Hewitt, though, who looked the sharper early on tonight, the South Australian breaking a shaky Djokovic in the fourth game of the match to open up a 4-2 lead.

He had another break-point opportunity the next game to forge a 5-2 advantage, but missed his big chance and then promptly dropped his own serve to love to allow Djokovic back on level terms.

It was the only invitation Djokovic needed, the third seed breaking Hewitt again in the 12th game to snare the opening set.

But Hewitt continued to play confidently and again claimed the first service break in the second set to go ahead 2-1.

Alas for Hewitt, Djokovic raised his level to reel off four straight games and jump out to a 5-2 lead before calmly closing out the set.

Djokovic, runner-up to Roger Federer at the US Open last September, motored through the third set with three more service breaks to set up a quarter-final against Spanish fifth seed David Ferrer.

Djokovic admitted suffering serious butterflies against Australia's last remaining singles hope, but felt he was able to exploit Hewitt's fatigue.

"The fact was Lleyton plays his best tennis at the Australian Open. He was very motivated to win it and I was very, very, very nervous," the 20-year-old said.

"But he was tired from his match against Marcos Baghdatis and I tried to seize the opportunity."

Hewitt's 12th unsuccessful Open campaign stretched his quarter-final drought to five grand slams.

Despite his most recent last-eight appearance at a major coming at the 2006 US Open almost 18 months ago, Hewitt said he maintained the hunger for more grand slam glory and that his epic five-set victory over Baghdatis had renewed his belief he could still mix it with the world's best.

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