Melbourne, Australia - After twice failing to win her breakthrough major as the No. 1-ranked woman at the Australian Open, Caroline Wozniacki is now expected to drop out of the top 10 after a fourth-round loss to a resurgent Svetlana Kuznetsova on Monday.

Wozniacki had the top ranking for the 2011 and 2012 editions of the season's first major, but lost in semifinals two years ago and the quarterfinals last year. Her 6-2, 2-6, 7-5 defeat to two-time Grand Slam winner Kuznetsova in the Round of 16 this time follows back-to-back first-round exits at Wimbledon and the U.S. Open.

Kuznetsova is moving in the other direction, after entering the tournament at No. 75. She's on a comeback from a right knee injury that ruled her out of the last U.S. Open, ending a run of contesting 40 consecutive majors.

The 27-year-old Russian moved into a quarterfinal and will next face either No. 1-ranked Victoria Azarenka or Elena Vesnina.

Play on Day 7 ran into Day 8 overnight, when Novak Djokovic needed just over 5 hours to beat Stanislas Wawrinka 1-6, 7-5, 6-4, 6-7 (5), 12-10 in a fourth-round match Sunday night, on the same court where he needed 5:53 to beat Rafael Nadal in last year's final.

"I just had flashback of 2012," said Djokovic, who ripped off his shirt to celebrate again, like he did last year. "It was maybe 45 minutes less this match than the one 12 months ago, but still it was still as exciting. I tried to enjoy the moment and couldn't ask for more. What a match point ... unbelievable."

The win was Djokovic's 18th in a row at Melbourne Park after winning the last two Australian titles, and earned him a place in the quarterfinals of a 15th consecutive major.

Wawrinka said he would take more positives than negatives out of the match. He led 5-2 in the second set after outplaying Djokovic in the first.

"For sure, I think the best match I have ever played," Wawrinka said. "I fought like a dog like always. At 4-4 in the final set, I thought I might have won the match, but he was just better."

Djokovic will next play No. 5 Tomas Berdych, who beat South Africa's Kevin Anderson 6-3, 6-2, 7-6 (13).

Fourth-seeded David Ferrer advanced 6-2, 6-1, 6-4 over No. 16 Kei Nishikori of Japan to set up a quarterfinal against fellow Spaniard Nicolas Almagro.

Roger Federer plays Milos Raonic later Monday, and U.S. Open champion Andy Murray faces Gilles Simon.

• Serena Williams may have rolled her ankle, and whacked herself in the lip with her racket, but that doesn't mean she needs any extra rest.

A day after winning her third-round match against Ayumi Morita of Japan - her first-injury free round at this year's Australian Open - the No. 3-ranked Williams was back on the court Sunday to play alongside sister Venus.

The Williams sisters take doubles seriously, and that can mean skipping the rest day between singles matches. Venus has joked they have so many trophies they use some as fruit bowls.

The sisters have captured 13 major doubles titles, including four at the Australian Open. They've also won three Olympic gold medals for doubles.

So dominant are Venus and Serena, they've never lost in a Grand Slam doubles final they've contested. They've reached the final in seven of the last 10 majors they've played.

"They mean a lot to me," Serena said earlier this week of her doubles titles from Grand Slams.

"I mean, people that are winning a lot of singles titles, nowadays, in the past decade or two decades, usually don't win as many in doubles. So I'm almost even with my singles and doubles."

Because they tend to only play doubles in the slams, the sisters don't have high rankings in the event. This means they usually have a low seeding - much to the chagrin of the top-ranked doubles teams in the world.

The Williams sisters were seeded 12th at the Australian Open, which led to an early third-round encounter with the unlucky fifth-seeded team of Nadia Petrova and Katarina Srebotnik on Sunday. The sisters won 6-2, 6-3.

Serena may be the more accomplished singles player in the family - Venus lost her second-round singles match to No. 2 Maria Sharapova - but on the doubles court she defers to her older sister.