Sharapova out as Nadal, Federer into last eight
Switzerland's Roger Federer plays a shot during his men's singles match against France's Jo-Wilfried Tsonga on day eight of the 2014 Australian Open tournament in Melbourne on January 20, 2014 - by Paul Crock
A day after Serena Williams' exit, Dominika Cibulkova kept the upsets rolling as she ousted injury-compromised Sharapova 3-6, 6-4, 6-1, blowing the women's draw even further open.
The main expected beneficiary, two-time defending champion Azarenka, is in position to take full advantage after she flattened old foe Sloane Stephens 6-3, 6-2 to reach the quarter-finals.
The Belarusian world number two will face Polish fifth seed Agnieszka Radwanska in the quarter-finals, with Cibulkova heading into a clash with Romania's Simona Halep.
Men's top seed Nadal weathered a sustained assault from Japan's Kei Nishikori 7-6 (7/3), 7-5, 7-6 (7/3) to face Grigor Dimitrov in the Bulgarian's first Grand Slam quarter-final.
The 13-time Grand Slam-winner chided the umpire after he was called for a time violation, for taking longer than the allowed 20 seconds between points, at a critical moment in the third set.
"The negative thing in my opinion is not the warning, but the timing of it. You can choose another moment to do it, not that one," Nadal said.
Wimbledon champion Andy Murray needed five match points and four sets -- and angrily demolished a racquet along the way -- before beating 'lucky loser' Stephane Robert.
Murray cruised through the first two sets but he missed match points, and then dropped his first set of the tournament, before finishing it off 6-1, 6-2, 6-7 (6/8), 6-2.
"He's a fun player to watch but not fun to play against," said Murray, as Robert milked applause from the crowd. "He made it very tricky for me, he plays all the shots very unorthodox."
Federer, meanwhile, was a convincing winner against Jo-Wilfried Tsonga, racing through 6-3, 7-5, 6-4 to set up a quarter-final against Murray.
There was some consolation for Sharapova when her boyfriend Dimitrov, 22, won 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 to Grand Slam tennis after months out with a right shoulder injury.
Sharapova blamed her tough workouts against Karin Knapp and Alize Cornet after a left hip injury flared against Cibulkova, who was motivated enough to take 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.
Cibulkova had never been beyond the fourth round in six previous attempts in Melbourne, although she has made the last eight at 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 after taking a medical timeout at a crucial moment.
Romania's Halep beat former women's number one Jelena Jankovic 6-4, 2-6, 6-0, in a result which added to the unfamiliar look of the women's quarter-finals.
Halep and Canada's Eugenie Bouchard are both in the last eight of a Slam for the first time, while neither Williams' conquerer Ana Ivanovic nor Flavia Pennetta are regulars.
In the final evening match, Poland's Radwanska saw off unseeded Spaniard Garbine Muguruza 6-1, 6-3 to reach the quarter-finals for the fourth year in a row.