Melborune: Last year's Australian Open finalist Dominika Cibulkova roared into the last eight on Monday, ending two-time champion Victoria Azarenka's comeback in a tight three setter.

The Slovak defeated the unseeded Belarusian 6-2, 3-6, 6-3 to set up a last eight clash with Serena Williams.

Serena Williams displayed all her fighting qualities to grind down the dangerous Garbine Muguruza and stay alive at the Australian Open.

The world number one battled back from a set down in a tense centre court match against the 24th seeded Spaniard to win 2-6, 6-3, 6-2 and make the quarter-finals, staying on track for a 19th Grand Slam title and her sixth at Melbourne.

(Photo: AP)

"I didn't start out so well and she did everything she needed to do in the first set," said Williams, who can lose her top ranking if she exits and Maria Sharapova wins the tournament.

"I just decided to do my best, stay focused and relax."

Williams was seen coughing throughout the match and confessed that "I've been a little sick in the last couple of days".

The 25-year-old Cibulkova, who lost last year's final to China's Li Na, went into the match as an underdog against Azarenka, who had defeated her seven times in their nine previous meetings.

But Cibulkova said her self belief blossomed as she stepped back onto Rd laver Arena, the scene of her best Grand Slam performance.

"I just walked on the court and all the memories came to my mind and I was just thinking 'I'm a great player, I can do it, I just have to believe in myself'," she said after the fiercly contested match.

Cibulkova had plenty to play for -- she has struggled at Grand Slams since last year's Australian Open and a loss would have sent her tumbling out of the top 20 for the first time since 2010.

Former world number one Azarenka, unseeded at Melbourne Park after returning from a horror 2014 when she struggled with injury and depression, looked shaky at times, conceding the first set with a double fault.

She switched tactics and rushed the net in the second set, also improving her serve, and reaped immediate rewards to take it 6-3 and force a decider.

The third set hung in the balance until the seventh game, when Cibulkova scored a decisive break and she went on to take the match and keep her dream of a first Grand Slam title alive.