Murray, Nadal lead the charge

Andy Murray, Serena Williams and Rafael Nadal led a charge into the fourth round of the Australian Open on Saturday as the focus switched back to tennis and away from ethnic clashes which had marred the "Happy Slam."

Police and security officers beefed up their presence at Melbourne Park after fighting between Serb and Bosnian ethnic fans on Friday and all aggression was restricted to the action on the courts.

Three-times former champion Williams coasted through with a 6-1, 6-4 win over China's Peng Shuai and sent an ominous reminder to her younger rivals why she remains the standard bearer of women's tennis.

"I'm feeling a little rusty, for whatever reason," Williams said. "It was definitely a lot better than my second round but I'm still trying to work on some things and hoping they'll come together."

Williams's next opponent will be Victoria Azarenka of Belarus, who sent former champion Amelie Mauresmo packing with a 6-4, 6-2 win.

Mauresmo, who won the Australian Open in 2006 when her semi-final and final opponents both retired injured, struggled to hold her serve against the in-form 19-year-old.

Azarenka broke six of Mauresmo's nine service games as she cruised to victory in 87 minutes, leaving the Frenchwoman rueing her missed opportunities.

"It's a little bit frustrating," Mauresmo said. "It's really the key points... that I didn't play good enough."

In the men's draw, British fourth seed Murray removed any doubts he was not a serious contender for the title with a 7-5, 6-0, 6-3 demolition of Austria's Juergen Melzer.

He next meets Fernando Verdasco.

"Against Verdasco, it's very important to use my head," Murray told reporters.

"I have a very good record against left handers. The only one I've lost to on the tour has been Nadal. I need to use my head, make him do a lot of thinking and moving.

"If I play like I did tonight, I can definitely win that one."

Top seed Nadal pummelled Tommy Haas 6-4, 6-2, 6-2 to reach the fourth round, showing no mercy in outgunning the German who had just returned to the tour after elbow problems.

"For sure I played my best match here. I'm very happy with my level today," Nadal said in a courtside interview.

"Probably I played my one of my best matches in Australia."

Last year's runner-up Frenchman Jo-Wilfried Tsonga advanced comfortably enough with a 6-4, 6-2, 1-6, 6-1 win over Israel's Dudi Sela.

Tsonga next meets ninth seed James Blake -- the American beat Igor Andreev of Russia 6-3, 6-2, 3-6, 6-1.

"Overall I was playing my kind of game: aggressive and taking time away from Igor, which I think is something you got to do," Blake said.

"If you let him set up and rip that forehand, he's going to hurt you pretty bad."

Spain's Carla Suarez Navarro proved her shock win over Venus Williams on Thursday was no fluke when she defeated compatriot Maria Jose Martinez Sanchez 6-1, 6-4.

Suarez Navarro will play another Spaniard, Anabel Medina Garrigues, in the fourth round.

Despite the bright sunshine in Melbourne it was a gloomy afternoon for the Bondarenko sisters from Ukraine.

Kateryna Bondarenko, the younger of the siblings, was crushed 6-2, 6-2 by China's Zheng Jie before Alona Bondarenko lost 7-6 6-4 to Svetlana Kuznetsova, one of six Russian women through to the last 16.

World number four Elena Dementieva kept up the Russian charge by beating local hope Samantha Stosur 7-6, 6-4.

France, attempting to get four men through to the round of 16, made a perfect start on Saturday when Gilles Simon and Gael Monfils both won in straight sets.

Simon, seeded sixth, beat Croatia's Mario Ancic 7-6, 6-4, 6-2 while 12th seed Monfils defeated Spain's Nicolas Almagro 6-4, 6-3, 7-5.

Richard Gasquet was unable to join his countrymen, though, as he let slip a two-set lead to fall to 13th-seeded Fernando Gonzalez, of Chile, 3-6, 3-6, 7-6, 6-2, 12-10.

Gonzalez meets Nadal next.