Second-seeded Roger Federer and Andy Murray stayed on course Monday for a semifinal in their half of the draw, with No. 1 and defending champion Novak Djokovic possibly waiting for the victor in next Sunday's final.
Serena Williams, chasing her third consecutive Grand Slam title, is still on course for a potential meeting with top-ranked defending women's champion Victoria Azarenka in the semifinals, with French Open champion Maria Sharapova, the top player in the other half of the draw, likely to be the opponent for the final.
With Djokovic and Sharapova advancing to the quarterfinals on Sunday, the other four easily won their fourth-round matches on Monday. Federer concluded the night session in Rod Laver Arena with a 6-4, 7-6 (4), 6-2 win over Canadian Milos Raonic, while Murray took advantage of Gilles Simon's ill health and fatigue for a 6-3, 6-1, 6-3 win.
Williams and Azarenka were even more dominant, losing just four games between them against their Russian rivals. The third-seeded Williams beat Maria Kirilenko 6-2, 6-0 and Azarenka defeated Elena Vesnina 6-1, 6-1.
Federer has won four of his record 17 major titles at Melbourne Park, where he has reached the semifinals or better every year since first winning the Australian Open in 2004.
The last time Federer failed to reach the last eight at a major was at the 2004 French Open, where he lost in the third round to Gustavo Kuerten. He next plays No. 7 Jo-Wilfried Tsonga, a finalist here in 2008.
"You try to win every match you can as quick as you can, saving energy in the process," said Federer, who has the benefit of experience. "At least you have a day in between, that's big."
Five months after he ended a 76-year drought for British men in Grand Slam tournaments with a win at the U.S. Open, Murray is on track to make it two in a row. He'll next play unseeded Frenchman Jeremy Chardy, who beat him the last time the pair met in Cincinnati last year.
Simon was coming off a tough five-set win over fellow Frenchman Gael Monfils.
"After the first few games, it didn't feel like that competitive," Murray said. "Sort of at this stage of a Grand Slam you're sort of geed up and prepared for a tough battle. That's why it becomes hard because the emotions aren't quite into it."
Simon said facing Murray was "a painful hour and a half on the court."
"It is difficult when you run a marathon two days before to run another one two days after," Simon said.
Chardy followed up 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. Tsonga, who lost the 2008 Australian Open final to Djokovic, plays Federer in the quarterfinals.
Djokovic had the day off Monday, but not really.
The top-ranked Djokovic needed 5 hours, 2 minutes to beat Stanislas Warwinka in a match that didn't end until the early hours of Monday, and he'll face No. 5 seed Tomas Berdych on Tuesday night.
There have been few such close matches on the women's side, where Sharapova, who plays Ekaterina Makarova in a quarterfinal Tuesday, has lost only five games in her first four matches. Williams hasn't dropped a set, and Azarenka has dropped just one.
Williams even surprised herself with her strong play against Kirilenko.
"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.
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.
"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.
She started last season with a 26-match winning streak, including a lopsided victory over Sharapova in the Australian Open final.
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."