MELBOURNE, Australia: All Serena Williams had to do was look at the numbers for an explanation of her stunning loss in the fourth round at the Australian Open.

Seven double-faults, including four in one game; 37 unforced errors, and a first-serve percentage of just over 50 percent Monday that had her convinced “maybe I should have started serving lefty.”

Some other numbers indicated why her 6-2, 6-3 loss to Russia’s Ekaterina Makarova on what she admitted was a still-sore left ankle was more of a shock, particularly at this stage of the year’s first major.

She has played 43 singles matches at Melbourne Park since she won the first of her five Australian Open titles in 2003, and Monday’s loss was just her third. She’s 54-7 since playing here for the first time in 1998, and she hasn’t gone out this early here since 2006.

“I’m not physically 100 percent, so I can’t be so angry at myself, even though I’m very unhappy,” Williams said. “I know that I can play a hundred times better than I did this whole tournament.”

Without Williams, who injured her left ankle in Brisbane two weeks ago, the only major winners still in contention were Maria Sharapova, defending champion Kim Clijsters and Wimbledon winner Petra Kvitova.

Sharapova earned the right to play Makarova in the quarterfinal when she beat Germany’s Sabine Lisicki 3-6, 6-2, 6-3 in a night match. The 2008 champion blew a 3-0 lead in the opening set, needed three set points to win the second and advanced on her second match point despite making 47 unforced errors and eight double-faults.

“A lot of ups and downs today – fortunately I finished on a high note,” she said. “Even though I didn’t play my best tennis I fought to the end and sometimes that’s what gets you through.”

Top-seeded Caroline Wozniacki, still in search of her first Grand Slam title, played Clijsters in a quarterfinal Tuesday. The Belgian advanced to the quarterfinals with a comeback win over Li Na Sunday in a rematch of the 2011 decider, while Kvitova had some trouble before beating former top-ranked Ana Ivanovic 6-2, 7-6 (2) Monday.

Kvitova will next play Sara Errani of Italy, who beat 2008 semifinalist Zheng Jie 6-2, 6-1.

In the late match, defending champion Novak Djokovic reached the quarterfinals for the fifth straight year with a 6-1, 6-3, 4-6, 6-3 win over former No. 1 Lleyton Hewitt.

Djokovic is aiming to become only the fifth man in the Open era to win three consecutive majors after winning Wimbledon and U.S. Open titles last year. He was up two sets and a break before Hewitt won six straight games to force a fourth set.

But after losing a set for the first time in the tournament, Djokovic regained his composure to ensure all of the top five men reached the quarterfinals. He will next play No. 5 David Ferrer, who had a 6-4, 6-4, 6-1 victory over Richard Gasquet of France.

Earlier, two-time runner-up Andy Murray was leading 6-1, 6-1, 1-0 when Mikhail Kukushkin retired from their fourth-round match with a left hip injury, giving Murray an easy path into the quarters.

“It’s obviously good for me, I get to conserve some energy,” Murray said. “Tough for him, first time in the fourth-round of a Slam.”

Murray will next play Kei Nishikori, who had a 2-6, 6-2, 6-1, 3-6, 6-3 win over sixth-seeded Jo-Wilfried Tsonga, the 2008 finalist.

The 22-year-old Nishikori became the first Japanese man in the last eight at the Australian Open in 80 years, and only the second man from his country to reach a Grand Slam quarterfinal since the Open Era started in 1968. Shuzo Matsuoka reached the 1995 Wimbledon quarterfinals.

“Feeling unbelievable. My first quarterfinal and beating Tsonga, makes me really happy,” Nishikori said. “I hope it’s big in Japan.”

Makarova, a 23-year-old Russian left-hander, was equally thrilled about her win over Williams. And considering she’d lost in the first round of the last six tournaments she’d played, in awe over who she beat.

“Yeah, I’m surprised because she’s a great player and it’s really tough to play against her. But, I don’t know, I just feeling so good and so focused,” Makarova said. “So I played my game, and that’s it. I won against Serena. That’s amazing.”

Makarova overcame plenty of crowd support for Williams. Oracene Price, Williams’ mother, was in the players’ box with her sunglasses on and a wide-brimmed hat.

In the fourth game of the second set with Makarova serving, Williams netted an easy forehand return. She made an angry sound, and there was a bit of laughter in the crowd. Price just turned away, shaking her head.

After Williams’ fourth double-fault in the fifth game of the second set, which gave Makarova the game and a 3-2 lead – Williams shouted “Oh, my God.” She looked ready to smash her racket, but in the end bounced it on the court and caught it on the rebound.

The 13-time Grand Slam winner had only played two competitive matches since losing the U.S. Open final to Sam Stosur in September, and her light preparation was curtailed when she badly twisted her ankle when she won her second-round match at Brisbane earlier this month.

For that reason, Williams was not about to beat herself up over her loss in Monday’s match.

“Am I usually angry? I don’t know. Crying? I don’t usually cry. So I don’t know what I usually project,” she said. “I feel like I didn’t play well at all today. I don’t really feel like I can’t get any better.”