MELBOURNE - Dominant Novak Djokovic swept into the Australian Open last eight Monday as the Williams sisters displayed fighting qualities to stay alive, but the tournament ended for two-time champion Victoria Azarenka.
The Serbian top seed was always in charge against unseeded Gilles Muller from Luxembourg, dictating terms in a testing 6-4, 7-5, 7-5 work-out to reach his eighth consecutive quarter-final at Melbourne Park.
He will now play big-serving Canadian eighth seed Milos Raonic as he bids for a fifth Australian crown and an eighth Grand Slam title.
"Generally it's a positive feeling. I haven't dropped a set, I'm in the quarter-finals," he said.
"There are a few things I think I can do better."
Raonic snuffed out the challenge of Spanish 12th seed Feliciano Lopez in five tough sets.
Fellow world number one Serena Williams battled back from a set down in a tense match against Spain's Garbine Muguruza to win 2-6, 6-3, 6-2, staying on track for a 19th Grand Slam title and her sixth at Melbourne.
"I didn't start out so well and she did everything she needed to do in the first set," said Williams, who can lose her top ranking if she exits and Maria Sharapova wins the tournament.
"I just decided to do my best, stay focused and relax. I think I've been playing for a long time. When I have to go up a level, I have to."
She will next face last year's finalist Dominika Cibulkova, the 11th seeded Slovak, who ended the comeback from injury of Azarenka in three tight sets.
Elder sister Venus' late-career renaissance gathered pace as she rolled back the years to thump Polish sixth seed Agnieszka Radwanska 6-3, 2-6, 6-1. She is now 9-0 for the season after winning the Auckland Classic.
It is the 34-year-old seven-time Grand Slam champion's first major quarter since the 2010 US Open, having been diagnosed with the energy-sapping Sjogren's Syndrome in 2011.
"The first set wasn't easy, in the second she just started to play better, in the third I think I went into a trance. I just wanted to win," she said.
Defending champion Stan Wawrinka ensured his passage by winning a thrilling fourth-set tiebreaker to down Spain's tenacious Guillermo Garcia-Lopez 7-6 (7/2), 6-4, 4-6, 7-6 (10/8).
He now plays Japanese superstar Kei Nishikori, who was a class above dogged Spanish baseliner David Ferrer, easing through 6-3, 6-3, 6-3.
"He's a tough, tough player. He improved a lot last year," Wawrinka said of Nishikori.