Melbourne: Serena Williams displayed all her fighting qualities to grind down the dangerous Garbine Muguruza and stay alive at the Australian Open Monday, but two-time champion Victoria Azarenka was bundled out.

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. "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.