The third-seeded Murray easily beat Gilles Simon of France 6-3, 6-1, 6-3 on Monday for his fourth straight-sets win in a row. He will play unseeded Frenchman Jeremy Chardy in the quarterfinals.
Simon, coming off a tough five-set win over fellow Frenchman Gael Monfils, clearly wasn't in any shape to challenge Murray.
"After the first few games, I mean, it didn't feel like that competitive," Murray said. "Sort of at this stage of a Grand Slam you're sort of gee'd up and prepared for a tough battle. That's why it becomes hard because the emotions aren't quite into it."
Serena Williams had a similarly easy time advancing to the quarterfinals and a chance to win her third major in a row with a 6-2, 6-0 win over Maria Kirilenko. She's still on course for a potential semifinal meeting with defending champion Victoria Azarenka, who advanced with a 6-1, 6-1 victory over Elena Vesnina.
"I didn't expect to come out and play so well tonight," Williams said. "I was like
'Wow!' I saw I had 95 percent first serves in the first set. I said 'Who is this girl?' It's not me usually."
Williams has lost only one match since her first-round exit at the French Open last year. Since then, she has won Wimbledon, Olympic gold, the U.S. Open, the season-ending WTA championships and a Brisbane International title.
Her 57-minute win over Kirilenko extended her current winning streak to 20 matches.
The 31-year-old Williams can become the oldest woman to hold the No. 1 ranking by winning her sixth Australian Open title. She next plays 19-year-old American Sloane Stephens, who reached the quarterfinals at a major for the first time with a 6-1, 3-6, 7-5 win over Bojana Jovanovski of Serbia.
Second-seeded Roger Federer, who could meet Murray in the semifinals, was playing Canadian Milos Raonoic in the second night match on Rod Laver Arena.
Chardy followed his upset of 2009 U.S. Open champion Juan Martin del Potro with a 5-7, 6-3, 6-2, 6-2 win over another highly-ranked player, No. 21 Andreas Seppi, in the fourth round.
Another Frenchman to advance was seventh-seeded Jo-Wilfried Tsonga, who beat friend and compatriot Richard Gasquet 6-4, 3-6, 6-3, 6-2 in the fourth round.
Tsonga, who lost the 2008 Australian Open final to top-ranked Novak Djokovic, could meet Roger Federer in the quarterfinals if the 17-time Grand Slam champion beats Canadian Milos Raonic later Monday at Rod Laver Arena.
Waiting on the other side of the draw is Djokovic, who could meet Federer or Murray in the final and plays his quarterfinal match Tuesday against Tomas Berdych. Djokovic advanced to the quarters after a 5-hour, 2-minute fourth-round win over Stanislas Wawrinka in the early hours Monday.
Azarenka's fourth-round win was as impressive as Williams'.
"It's getting there ... with every match you start building up for the top battles starting now," said Azarenka, who needed only 57 minutes to beat the 47th-ranked Vesnina. "It's really exciting to be again so far in the tournament."
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Azarenka started last season with a 26-match winning streak, including a lopsided victory over Maria Sharapova in the Australian Open final. She moved to No. 1 in the rankings with that win and has remained there for all but a few weeks ever since.
But she needs to defend her Australian title to prevent French Open champion Sharapova or Williams from claiming No. 1.
Next up for Azarenka is a quarterfinal against Svetlana Kuznetsova, who entered the season's first major ranked No. 75 but has won titles at the 2004 U.S. Open and 2009 French Open.
After five breaks of serve in the third set, Stephens broke Jovanovski and then held to advance
-- knowing her parents and grandparents were watching on TV.
"I'm sure my mother's had like four heart attacks," Stephens joked after the see-saw match. "I hope my Grandpa didn't have to put my Grandma to bed, because she gets a little worried."
Williams, who has rated Stephens a potential world No. 1, beat the 19-year-old American in straight sets two weeks ago at the Brisbane International, one of the warm-up tournaments for the Australian Open.
Stephens is looking forward to a rematch, where there won't be any major surprises.
"It will be tough, obviously ... it's quarters of a Grand Slam," she said. "There won't be that like first time,
'Oh, my God, I'm playing Serena'. That's kind of out of the window now. So that's good. And then it will feel more of like a regular match instead of all the other like things to think about."
Kuznetsova was given a time warning for taking too long during a changeover in her 6-2, 2-6, 7-5 win earlier Monday over former No. 1 Caroline Wozniacki, but said it didn't bother her.
As for Wozniacki, after twice failing to win her breakthrough major as the No. 1-ranked woman at the Australian Open, she is now expected to drop out of the top 10 after a fourth-round loss that follows back-to-back first-round exits at Wimbledon and the U.S. Open.
Kuznetsova is moving in the other direction on her comeback from a right knee injury that ruled her out of the last U.S. Open, ending a run of contesting 40 consecutive majors. And she's looking forward to taking on Azarenka.
"The time I played in Indian Wells was totally a disaster. I got (beaten) very badly," she said. "But, I mean, she's tough. She's No. 1. I have nothing to lose. She has all the pressure.
"I know I got the game to give her some problems, and I will just do my best and just try to enjoy it."
Press; By DENNIS PASSA]
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