Fancied fourth seed Andy Murray [Images] suffered a fair-and-square five-set defeat at the Australian Open [Images] after almost half Monday's field had reached the quarter-finals when their opponents retired injured or ill.

Serena Williams [Images], Svetlana Kuznetsova [Images] and Gilles Simon all eased into to the last eight of their draws without having to complete their matches but Murray, one of the favourites before the tournament, fell 2-6 6-1 1-6 6-3 6-4 to Fernando Verdasco.

"I had my chances," the Scot shrugged. "He served incredible in the fourth and fifth sets. So he deserves the credit for the win.

"Sometimes you've just got to say 'too good', and he played better than me."

Spaniard Verdasco faces Jo-Wilfried Tsonga next after last year's finalist beat James Blake [Images] 6-4 6-4 7-6.

Murray had been bidding to become the first British men's grand slam champion since Fred Perry won Wimbledon [Images] and the U.S. Open in 1936 but, like so many British hopes before him, he flattered to deceive.

"It's not a disaster," Murray said. "I'm still playing well. I lost to a good player in a very close match. I'll have more chances to win grand slams," last year's U.S. Open runner-up added.

World number one Rafa Nadal breezed through 6-3 6-2 6-4 over Fernando Gonzalez [Images], avenging a heavy loss to the Chilean here in 2007.

"I think I played well. Very solid match from the baseline," Nadal said. "Playing very good forehands, backhands. I am improving." Next up for the Spaniard is sixth seed Simon.

Gael Monfils and Zheng Jie waved Simon and Kuznetsova through early in the day by pulling out with wrist injures while women's second seed Williams advanced when Victoria Azarenka staggered off centre court in tears, off-balance and barely able to hold her racket.

Thirteenth-seeded Azarenka had been leading 6-3 2-4 but finally quit in tears after unsteadily patrolling the baseline for several points.

Azarenka needed to be assisted off court by two trainers, supporting her either side.

FEELING SICK

"Well I just woke up this morning feeling sick already, threw up all morning," the Belarussian said. "Very disappointing for me.

"They think it was a virus or something... whatever happens, happens. There was not much I could do about it."

Three-times champion Williams will play Russian Kuznetsova in the quarters after Zheng retired with a wrist injury.

"Only the strongest are blessed," said Kuznetsova, who led 4-1 in the first set when Zheng threw in the towel. "You know, the saying? We say it in Russian.

"I was winning. It was no problem. I felt great. Either way for me was good. But I felt sorry for her because she was in great shape."

Sixth seed Simon suffered a bittersweet experience, advancing to the quarters after friend and fellow Frenchman Monfils was forced to retire with a wrist injury.

Simon had been leading 6-4 2-6 6-1 when Monfils, who had been continuously flexing and shaking his right hand throughout the match, called a halt to proceedings.

Monfils, the 12th seed at Melbourne Park, had received treatment on his right wrist during the third set and then had it strapped before the fourth began.

"Well, you never want to win like this," Simon told reporters. "It's already strange when it's another player, but when it's a friend like Gael it's more difficult."

The 24-year-old Simon said he had chatted after the match to his fellow "New Musketeer," who said he was in pain.

"When I really felt it was at 3-1 for Gilles," said Monfils. "It was maybe 3-0 (in the third set and) I served, that service game, then I started to feel it.

"I FEEL IT"

"Then I asked the physio. I was thinking maybe it was (in) my head. Then I said, 'I feel it'."

Elena Dementieva [Images] stretched her winning streak to 14 matches when she demolished Slovakia's Dominika Cibulkova 6-2 6-2 to advance.

The Russian fourth seed now meets the dangerous unseeded Spaniard Carla Suarez Navarro, who knocked out sixth seed Venus Williams [Images] earlier in the tournament, in the quarter-finals.

"I think she's a very tough player," the Russian said.

"She plays a very unique style of game. A lot of spin. It's gonna be a tough match."

Suarez Navarro beat fellow Spaniard Anabel Medina Garrigues 6-3 6-2.

The 20-year-old, who speaks only a few words of English, is one of two unseeded women through to the last eight, along with Australian Jelena Dokic [Images].

• Complete tennis coverage
• All you want to know about Sania Mirza