World number one Lleyton Hewitt continued his miserable run at the Australian Open with a shock defeat to Morocco's Younes El Aynaoui.

The Australian - who has never made the last eight at his home Grand Slam - lost the fourth-round encounter 7-6 6-7 7-6 6-4.

"It's tough at the moment but I'm not going to get too dejected about it," said Hewitt.

He kept hitting the lines and I couldn't get any rhythm on my returns Lleyton Hewitt

"It could make me a bigger, stronger person when I come back to play in the years to come."

It took until midway through the fourth set for the first break of serve, with El Aynaoui taking the seventh game as Hewitt double-faulted.

And there was no way back for the top seed as El Aynaoui served out the match for the biggest win of his career.

Hewitt could not break the Moroccan's serve

The 31-year-old Moroccan, the oldest first-time winner on the ATP Tour, consistently matched the Australian in a high-quality match.

He allowed Hewitt only three break points, and rattled off 75 winners during three-and-a-half hours of absorbing tennis.

"There was one break of service in four sets of high intensity tennis," Hewitt noted afterwards. "It's just disappointing that I was at the other end of it.

"I had a lot of chances but he served huge. He kept hitting the lines and I couldn't get any rhythm on my returns. He was too good."

The momentum swung El Aynaoui's way in the third-set tie-breaker when a series of big forehands earned a set point at 6-5.

Hewitt found the net with a forehand to hand the set and a decisive advantage to the Moroccan.

The pressure on Hewitt's serve finally told when he double faulted on break point at 3-3 in the fourth set.

Serving for the match, El Aynaoui double faulted himself to give Hewitt a glimmer of hope as the home favourite forced a break point, but the Moroccan held on.

"I served well the whole way. That's the most difficult thing for me - to keep a very high level of play during four or maybe five sets," said El Aynaoui.

"And today I did it. Lleyton helped me a little bit. I don't think he played his best today.

"I saw I had a chance and I took the opportunity."