MELBOURNE, Australia -- Victoria Azarenka advanced to the quarterfinals and firmed as a favorite to claim a third straight Australian Open title on Monday after Maria Sharapova joined Serena Williams on the fourth-round casualty list.
Azarenka had a 6-3, 6-2 win over No. 13-seeded Sloane Stephens in a match that didn't have any of the drama of their contentious semifinal here last year.
Third-seeded Sharapova lost 3-6, 6-4, 6-1 to Dominika Cibulkova in the earlier match on Rod Laver Arena, struggling with her serve in the second and third sets and making 45 unforced errors as she tried to claw her way back.
Her serve started to backfire from the eighth game, when she was broken at love while trying to serve out the first set.
During a run of four breaks against her, Sharapova won only three points on her own serve and fell 5-0 behind in the second set.
The four-time major winner rallied to win four straight games before Cibulkova held to level the match. After taking an off-court medical time out after the second set for a hip strain, she was broken immediately and had seven double-faults in the third set.
Sharapova was two tournaments into a comeback from a prolonged layoff with a right shoulder injury, and said her run to the fourth round was a positive sign because she was healthy and back on tour.
"I have to look at the positives and see where I have come from in four or five months. I haven't played a lot of tennis in those six months," said Sharapova, who won the Australian title in 2008 and lost two other finals.
"So I certainly would have loved to play a little bit more before playing a Grand Slam, but this is the chance that I was given."
Top-ranked Williams, a five-time Australian Open champion, was knocked out in a three-set loss to 14th-seeded Ana Ivanovic on Sunday, and later revealed she had a back problem that had her considering withdrawing from the tournament.
Another former No. 1 was knocked out when No. 11 Simona Halep beat Jelena Jankovic 6-4, 2-6, 6-0 to set up a quarterfinal against Cibulkova.
Sharapova may stick around in Melbourne to support her boyfriend, Grigor Dimitrov, who reached the quarterfinals for the first time with a 6-3, 3-6, 6-2, 6-4 win over Roberto Bautista Agut. The 22-year-old Bulgarian will next play the winner of Monday's later match between top-ranked Rafael Nadal and No. 16 Kei Nishikori of Japan.
Azarenka, meanwhile, was making herself comfortable at Melbourne Park, where she's on an 18-match winning streak.
"I just love playing here, the surroundings, it feels so cozy ... feels like home," she said after her win over Stephens. It was a rematch of their semifinal last year when Azarenka took a medical timeout just when it appeared Stephens was getting momentum, then came back and won the match.
In the first set, Stephens accidently hit Azarenka in the hip area with a shot at the net, and Azarenka sent a forehand whizzing past Stephens a few games later.
There was very little tension, though, after Azarenka broke Stephens' serve to open the second set and then again to take a 5-2. The second-seeded Azarenka didn't' have any trouble closing out this time, saving one set point before setting up match point with an ace.
Sharapova made it hard for herself in Australia, having difficulty closing out her second- and third-round matches. She needed almost 3 1/2 hours to beat Karin Knapp in searing heat the second round - playing 50 minutes between her first and final match points. She said she couldn't use the heat wave as an excuse for her loss, and added that the hip strain wasn't anything out of the ordinary for a tennis player.
Cibulkova had spent just over 3 1/2 hours on court in her first three wins.
The pair hadn't played since Sharapova's quarterfinal win at Wimbledon in 2011. Now they're evenly split in six head-to-heads, but Cibulkova has won two of their three matches at the majors with her win Monday and her quarterfinal victory at the 2009 French Open.
"I was never doubting myself," the No. 20-seeded Cibulkova said, adding that Ivanovic's win over Williams the previous day had been motivational but not her main inspiration against Sharapova.
"This was a different story. I already beat Maria before, and I beat her" at a Grand Slam tournament.