Maria Sharapova joined Serena Williams as fourth-round casualties, leaving Azarenka a potentially easier run to the women's final. Sharapova was beaten by No. 20 Dominika Cibulkova in the match on Rod Laver Arena immediately before Azarenka defeated Sloane Stephens, the last remaining American in the singles draw.

Nadal won three tough sets against Kei Nishikori, while Murray wasted four match points in the third set - including two in the tiebreaker - before dominating the fourth set against lucky loser Stephane Robert of France.

Four-time Australian champion Roger Federer was playing 2008 finalist Jo-Wilfried Tsonga in a late match, with the winner moving into a quarterfinal match against Murray.

Third-seeded Sharapova, complaining of a hip ailment, lost 3-6, 6-4, 6-1 after struggling with her serve and made 45 unforced errors. She joins Serena Williams on the sidelines after the top-ranked American lost in three sets Sunday to Ana Ivanovic, ending 25-match winning streak.

Sharapova spent the latter months of last year on the sidelines with a right shoulder injury, so wasn't expecting much of herself.

''I have to look at the positives and see where I have come from in four or five months,'' Sharapova said. ''I haven't played a lot of tennis. I certainly would have loved to play a little bit more before playing a Grand Slam, but this is the chance that I was given.''

Azarenka had a 6-3, 6-2 win over No. 13-seeded Stephens, the player who beat Williams in the quarterfinals here last year and then lost to Azarenka in the semifinals under controversial circumstances. Azarenka took a medical time out when Stephens started to take momentum in that match, then came back to advance to the final and subsequently her second Australian Open trophy.

She wasn't getting carried away Monday with the apparent ease of the draw with Williams and Sharapova gone.

''The players who beat those players deserve all the credit because they've been better, so they are dangerous and they are competitive,'' Azarenka said.

Nadal beat Nishikori 7-6 (3), 7-5, 7-6 (3) and was broken twice in the third set - getting a time violation from chair umpire Evanthia Asderaki in one of them. The 13-time major winner tripped in the first set and tumbled to the court, then had to go to the locker room to change shoes.