Sharapova out as shocks keep rolling at Australian Open
Belarus's Victoria Azarenka plays a shot during her 4th round match against Sloane Stephens of the US, on day eight of the Australian Open tournament, in Melbourne, on January 20, 2014 - by Saeed Khan
The diminutive Slovakian enjoyed one of the biggest wins of her career, 3-6, 6-4, 6-1, a result which also did a big favour for defending champion Victoria Azarenka.
Azarenka, now the hot favourite as she guns for a rare hat-trick of Australian Open wins, stepped up her bid when she flattened old foe Sloane Stephens 6-3, 6-2.
"I'm glad I could find my rhythm and go for my shots. I just love playing here. It feels so cosy, it feels like home," Azarenka said.
The Belarusian world number two will face either Agnieszka Radwanska or Garbine Muguruza in the quarter-finals, with Cibulkova heading into a clash with Romania's Simona Halep.
With Sharapova, the Russian world number two, and top seed Williams both out, the women's last eight has an unfamiliar feel.
Halep and Canada's Eugenie Bouchard are both first-time Slam quarter-finalists, while neither Williams' conquerer Ana Ivanovic nor Flavia Pennetta are regulars at the business end.
There was some consolation for Sharapova when her boyfriend, Grigor Dimitrov, reached his first Grand Slam quarter-final 6-3, 3-6, 6-2, 6-4 against Roberto Bautista Agut of Spain.
But overall it was a dismal day for the statuesque Russian, cutting short what has been a difficult return from months out with her troublesome right shoulder injury.
Sharapova blamed her tough workouts against Karin Knapp and Alize Cornet after a left hip injury flared against Cibulkova, who was fit and motivated enough to take full advantage.
Sharapova was too strong for Cibulkova in the first set but errors crept in in the second and after the Slovak levelled at a set each, she left the court for a medical timeout.
And Sharapova, rated as the world's highest paid female athlete, succumbed tamely in the third set as she conceded three breaks to keep her search for a fifth major title on hold.
"I think it's a success (the tournament) in terms of that I'm back and that I'm healthy. That's quite important. Otherwise I wouldn't give myself a chance to play," she said.
"So on that note, yeah, 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."
Cibulkova had never been beyond the fourth round in six previous attempts in Melbourne, although she has made the last eight at all the other three Grand Slams.
"I was 100 percent sure I could win. I never doubted myself even when I lost the first set," said the 20th seed. "I knew what I needed to do. The most important thing is to believe in yourself."
Azarenka later coasted past Stephens, erasing memories of last year's semi-final when she was accused of gamesmanship and slow-handclapped by the crowd after taking a medical timeout at a crucial moment.
Men's number one Rafael Nadal was on court against Kei Nishikori, with Roger Federer playing Jo-Wilfried Tsonga and Andy Murray against lucky loser Stephane Robert later.
The men's doubles was also rocked by an upset on Monday when top-seeded American twins Bob and Mike Bryan, with a record 15 Grand Slam titles, went out in the third round.