MELBOURNE, Australia — Gilles Simon advanced to the Australian Open quarterfinals Monday when fellow Frenchman and longtime friend Gael Monfils retired after three sets.

Sixth-seeded Simon was leading 6-4, 2-6, 6-1 when No. 12 Monfils withdrew with what appeared to be an injured right hand or arm.

Monfils, a semifinalist at the French Open last year, had treatment in the previous set and, after going to the baseline following the change of ends, walked to the net and told Simon he could not continue.

The pair hugged at the net and kissed each other's cheek. Despite being close in age — Simon is 24, Monfils is 22 — it was their first match at tour level.

"It's very hard, because we're very close," Simon said in an on-court interview. "I didn't want to win like this. Sorry everybody, that's not the way you want to win."

Simon, into the second week of a major for the first time, next plays top-ranked Rafael Nadal or 2007 Australian Open runner-up Fernando Gonzalez.

"The last time against Rafa it was good for me," he said of his October win over Nadal in the Madrid semifinals. But, "he beat me here in three sets last year.

"If it's him, it's going to be hard. If it's Fernando, it's going to be the same."

In the opening women's match, Carla Suarez Navarro reached the quarterfinals after a 6-3, 6-2 win over No. 21 Anabel Medina Garrigues in an all-Spanish match.

Suarez Navarro, who had an upset win over seven-time Grand Slam winner Venus Williams in the second round, next plays Olympic gold medalist Elena Dementieva.

Saurez Navarro went through qualifying at the French Open last year and made the quarterfinals in her Grand Slam debut.

Dementieva had a 6-2, 6-2 win over Slovakia's Dominika Cibulkova to reach the quarterfinals at Melbourne for the first time in 11 years.

The fourth-seeded Dementieva, who won two titles coming into the season's first major, extended her winning streak to 14 matches on Monday.

A finalist at the French and U.S. Opens in 2004, Dementieva has never been back to a championship match. She was ousted in the quarterfinals at the French last year and reached the semifinals at Wimbledon and the U.S. Open.

Second-seeded Serena Williams, seeking a 10th Grand Slam singles title, was to play No. 13 Victoria Azarenka of Belarus at Rod Laver Arena. The winner will meet No. 8 Svetlana Kuznetsova, who advanced when No. 22 Zheng Jie of China retired while trailing 4-1.

Kuznestova, the 2004 U.S. Open champion, and Williams are the only major winners remaining in the women's draw.

Zheng needed treatment on her left thumb and hand after she tumbled and tried to break her fall with her hand after the third game. She withdrew two games later.

Roger Federer, trying to equal Pete Sampras' record 14 Grand Slam singles titles, had a narrow fourth-round win over Tomas Berdych on Sunday.

On the court where women's No. 1 Jelena Jankovic was knocked out in the day's opening match and No. 3 Dinara Safina had to save match points before advancing, Federer also appeared in trouble.

Not in his mind.

"I wasn't thinking of losing, that's for sure," Federer said after reaching the quarterfinals with a 4-6, 6-7 (4), 6-4, 6-4, 6-2 win. "The finish line was still very far for Tomas. I knew that.

"He pushed me to the limit. You've got to hang in there, there's no other solution."

He next faces 20-year-old Juan Martin del Potro, seeded eighth from Argentina, who advanced 5-7, 6-4, 6-4, 6-2 over No. 19 Marin Cilic of Croatia.

Defending champion Novak Djokovic of Serbia jumped to a 5-0 lead, then was pushed the rest of the way in a 6-1, 7-6 (1), 6-7 (5), 6-2 victory over 2006 runner-up Marcos Baghdatis of Cyprus in a match that finished at 2:26 a.m. Monday.

He'll next play American Andy Roddick, who ousted No. 21 Tommy Robredo 7-5, 6-1, 6-3.

The top eight seeds in the men's draw made it to the fourth round here for the first time since 1970.

As well as No. 1 Nadal, No. 4 Andy Murray and No. 5 Jo-Wilfried Tsonga were in action later Monday.

If the top eight reach the quarters, it will be a first in a Grand Slam in the Open era.