-- MELBOURNE, Australia -- With Maria Sharapova following Serena Williams out of the Australian Open in the second upset in 24 hours, attention turned quickly to defending champion Victoria Azarenka's bid for a third consecutive title.
Sharapova lost 3-6, 6-4, 6-1 to Dominika Cibulkova in a fourth-round match Monday 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.
Top-ranked Williams lost to Ana Ivanovic on Sunday afternoon, ending her 25-match winning streak and taking the hottest of title contenders out of the draw.
Losing the rivals ranked Nos. 1 and 3 in quick succession didn't distract No. 2 Azarenka, who had a 6-3, 6-2 win over No. 13-seeded Sloane Stephens in a match that lacked the drama of their contentious semifinal here last year.
Both Azarenka and Stephens have vigorously denied any lingering tensions and publicly, at least, heaped praise on their rival player's talents.
"Sloane is a great player, a very tough fighter," Azarenka said after the match. She also denied being ruffled by a body blow from a huge Stephen's forehand in the first set that hit her hard below the waist: "Why would I have a problem with that? That's tennis."
"The players who beat those players deserve all the credit because they've been better, so they are dangerous and they are competitive," Azarenka said. "For me it's important to just keep focusing on my game. Quarterfinals of a Grand Slam are never easy, no matter who you play."
For Stephens, the loss marked the exit of the last American from the singles draw.
The rising American star who has excelled on big stages in the past -- last year she beat Serena Williams in the quarterfinals here -- praised Azarenka's aggressive game.
"She's obviously No. 2 in the world," said Stephens. "She's just a really tough competitor."
Third-seeded Sharapova's serve started to backfire from the eighth game, when she was broken at love while serving for the 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 No. 20-seeded 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."
The four-time major winner made it hard for herself in Australia, needing almost 3½ hours to beat Karin Knapp in searing heat the second round -- playing 50 minutes between her first and final match points.
Cibulkova had spent just over 3½ hours on court in her first three wins, and went in confidently knowing she'd beaten Sharapova in a Grand Slam quarterfinal before.
"I was never doubting myself," Cibulkova said, who completed a full set of Grand Slam quarterfinal appearances with her best run yet in Melbourne. She'll next play first-time Grand Slam quarterfinalist Simona Halep, who beat former No. 1-ranked Jelena Jankovic 6-4, 2-6, 6-0.
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 top-ranked Rafael Nadal, who defeated No. 16 Kei Nishikori of Japan.
Azarenka, meanwhile, was making herself comfortable at Melbourne Park, where she's on an 18-match winning streak. She had her singer boyfriend Red Foo in the stands, and could joke about engagement rings -- which she hasn't got -- in her on-court post-match interview.
"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.
The Associated Press contributed to this report.