At least Caroline Wozniacki won't have to answer questions about her World No. 1 ranking anymore.

Wozniacki, who has spent 67 of the last 68 weeks atop the world rankings despite never winning a major championship, lost in straight sets to defending Australian Open champion Kim Clijsters in the quarterfinals on Tuesday.

The 6-3, 7-6 (7-4) decision means Clijsters still has a chance to become the eighth women's player to successfully defend the Australian Open title and also ensures a new World No. 1 by week's end.

Clijsters, seeded 11th, reached the quarters only after rallying past Li Na on Sunday in a rematch of last year's title match in Melbourne. The Belgian suffered an ankle injury in the first set, then saved four match points in the second-set tiebreaker before staving off Li in the third.

The four-time Grand Slam champion had decidedly less trouble Tuesday, earning six breaks of serve at Rod Laver Arena.

Wozniacki was able to force a tiebreaker in the second set, but a cross-court winner gave Clijsters match point at 6-4. As was the case for most of the match, Wozniacki was unable to win a point on her serve, as Clijsters' winner at the net sent the Dane home early yet again.

Wozniacki had not dropped a set in her first four matches at the season's first major, but won just 49-percent of her service points to fall to 0-3 in her career against Clijsters.

In the semifinals, Clijsters will meet Victoria Azarenka, who overcame a letdown in the first-set tiebreaker to upend Agnieszka Radwanska 6-7 (0-7), 6-0, 6-2 in their quarterfinal match.

There were eight breaks of serve in the first set alone between Azarenka and the eighth-seeded Radwanska, who won all seven points in a surprisingly quick tiebreaker.

Azarenka, seeded third, bounced back from losing her first set of the tournament quite swimmingly, goose-egging the Pole in a 26-minute second set.

The Belarussian kept the momentum in her favor and controlled the final set to improve to 7-3 against Radwanska, who has yet to reach a major semifinal. Azarenka reached her second Grand Slam semi.

The other two quarterfinal matches will be played on Wednesday, with Ekaterina Makarova, fresh off an upset of Serena Williams, taking on fourth-seeded Maria Sharapova and second-seeded Petra Kvitova squaring off against Sara Errani.

Either Azarenka, Kvitova or Sharapova will take over the No. 1 ranking.