MELBOURNE, Australia (AP) — Two-time defending champion Victoria Azarenka saw another of her main adversaries crash out of the Australian Open yesterday, while top-ranked Rafael Nadal and Wimbledon champion Andy Murray faced tougher-than-expected matches to advance to the quarter-finals at Melbourne Park.

Maria Sharapova joined Serena Williams as fourth-round casualties, leaving Azarenka a potentially easier run to the women’s final. Sharapova was beaten by number 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 Open champion Roger Federer was never threatened in beating 2008 finalist Jo-Wilfried Tsonga 6-3, 7-5, 6-4 in a late match. He will play Murray in the quarter-finals tomorrow.

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

Sharapova had spent the latter months of last year on the sidelines with a right shoulder injury, so she 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. “

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

She wasn’t getting carried away yesterday 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.

Azarenka, who is on an 18-match winning streak at Melbourne Park, will next play number 5 Agnieszka Radwanska, who beat Spain’s Garbine Muguruza 6-1, 6-3 in the final fourth-round match last night.

Nadal beat Nishikori 7-6 (3), 7-5, 7-6 (3), though he was broken twice in the third set — getting a time violation from chair umpire Evanthia Asderaki in one of the games.

“Normally I have a good self-control on court, and it’s true that the moment was a very critical one,” Nadal said of the time violation.

The 13-time major winner also tripped in the first set and tumbled to the court, then had to go to the locker room to change shoes.

Nadal next plays Grigor Dimitrov, who reached the quarter-finals of a Grand Slam for the first time with a 6-3, 3-6, 6-2, 6-4 win over Roberto Bautista Agut.

Three-time Australian Open finalist Murray ended the run of Robert, wasting match points in the third set and smashing his racquet after the tiebreaker before advancing 6-1, 6-2, 7-6 (6), 6-2.

“He’s a fun player to watch, but not a fun player to play,” Murray said of Robert’s assortment of drop shots and deft groundstrokes.

The racquet smashing was pure frustration.

“Losing that set was frustrating because it obviously means you’re out there another 30, 40 minutes at least, when I would preferably had been in the locker room,” Murray said. “My racquet bit the dust. Unfortunate for it.”

Murray said he’s expecting a tough match against Federer, regardless of the Swiss player’s recent drop in the rankings that has seen him seeded sixth here.

“I think last year you could see at periods he was struggling with his back,” Murray said. “And if he’s fully fit, I’ve said all along, he’s always going to be there or thereabouts in the majors, and he’ll give himself opportunities to win more because he’s that good.”