Maria Sharapova followed Serena Williams out of the Australian Open after losing in the fourth round to Dominika Cibulkova.

Like world number one Williams, who struggled with back problems during her defeat by Ana Ivanovic on Sunday, Sharapova appeared hampered physically during her 3-6 6-4 6-1 defeat. 

The third seed required off-court treatment after dropping the second set and there was no way back. 

Sharapova had not had an easy time of it during the first three rounds, most notably a three-and-a-half-hour battle in extreme heat against Karin Knapp in round two. 

She admitted after struggling past Alize Cornet in the third round that she still felt rusty following the shoulder problems that brought an early end to her 2013 season. 

Initially things looked much better for the Russian on Monday as she broke the Cibulkova serve in the first game. 

Her serve has been wobbly and she dropped it serving for the opening set but responded with another break of Cibulkova's to take it. 

Slovakian Cibulkova had caused Sharapova problems in the past, winning two of their previous five meetings despite giving away nearly a foot in height. 

And the 24-year-old was soon on the offensive in the second set, winning five games in a row as the Sharapova's unforced error count began to climb rapidly. 

But one thing the Russian never lacks is fight, and instead of moving on to the decider, Sharapova battled, clawing back four games. 

She could not complete the job, though, Cibulkova recovering from a double fault on her first set point to finally clinch it on her second. 

Sharapova then called the trainer and left court, with the problem not immediately obvious, although she was clearly struggling with her movement. 

Cibulkova took advantage with an immediate break of the Sharapova serve at the start of the deciding set and, although the third seed staved off break points in the third game, she was barely hanging on. 

Cibulkova broke again to lead 4-1 and this time there was not even a hint of a comeback from Sharapova. 

The 20th seed is through to her first Australian Open quarter-final and will play Romania's Simona Halep, who reached her first grand slam quarter-final with a 6-4 2-6 6-0 win over eighth seed Jelena Jankovic. 

Halep won six titles last season, more than anyone except Williams, and will break into the top 10 at the end of this tournament.

The exits of Sharapova and Williams - beaten by Ana Ivanovic on Sunday - left second seed Victoria Azarenka as the clear favourite to win her third straight Australian Open title.

Azarenka secured a second win over Sloane Stephens at the Australian Open but in far less controversial circumstances.

Azarenka is now a clear favourite to win her third straight title in Melbourne following early exits for Williams and Sharapova, and the Belarusian looked very solid in a 6-3 6-2 victory to move through to the quarter-finals.

Twelve months ago the pair met in the last four and Azarenka found herself a hate figure for the Melbourne crowd after taking a long injury time-out with Stephens about to serve to stay in the match.

Azarenka had missed five match points in the previous game and in her on-court interview she joked she had almost committed "the choke of the year" against a teenager in her first grand slam semi-final.

Azarenka later insisted the break had not been tactical and she had in fact been treated for a rib problem that was making it hard for her to breathe but the damage was done.

Both players were keen to keep the past in the past in the build-up to the rematch, but it was clear there is no love lost.

They share an agent and, asked what their off-court relationship was like, Stephens replied: "Non-existent".

The animosity bubbled to the surface during the seventh game of the match when Stephens chased down a drop shot and aimed her reply straight at her opponent.

She held her racket up in apology but a few points later Azarenka responded with a volley close to Stephens' head. The 20-year-old simply smiled and clapped her hand against her racket.

Mostly Azarenka was too in control of the match for there to be much tension.

The second seed broke the Stephens serve for 3-1 and mostly it was the young American fighting to stay in touch.

Azarenka was given a time violation serving for the set at 5-3 but won the next two points to clinch it, and she began the third set with an immediate break.

Stephens has made the second week at five successive grand slams and she battled hard to hold on to her serve to make it 2-3.

But Azarenka was relentless and a break for 5-2 meant the end was swift in coming.