(CNN) -- Caroline Wozniacki's quest for a first grand slam title and her reign as world No. 1 both ended on Tuesday after a quarterfinal defeat by defending champion Kim Clijsters at the Australian Open.
Four-time grand slam winner Clijsters showed little sign of being hampered by the ankle injury she sustained during her fourth-round win against last year's runner-up Li Na as she won 6-3 7-6 (7-4) in one hour and 45 minutes.
Wozniacki finished the last two seasons top of the world rankings and has been No. 1 seed for the last six majors. However, the 21-year-old Dane is now certain to fall below No. 2 Petra Kvitova and No. 3 Victoria Azarenka -- who is Clijsters' semifinal opponent on Thursday.
Fourth seed Maria Sharapova, who plays fellow Russian Ekatarina Makarova in the last eight on Wednesday, could also take top spot -- a position she, like Clijsters, has held before.
"Kim is very experienced," Wozniacki, who was beaten by Clijsters in her only grand slam final at the 2009 U.S. Open, told reporters.
"I mean, she's a great player. Of course I really don't like losing. I try to go in and try to win every time I play, but today Kim was just that little bit better than me."
Wozniacki, who could slip to No. 4 in the world depending on Sharapova's results, insisted she is not concerned about losing her top ranking.
"I start laughing every time because the media talks to me like I'm finishing my career and I only have one year left and time is running out," she said.
"I still have a number of Australian Opens and a number of U.S. Opens and Wimbledons and French Opens left.
"In the end of the day, you can just do your best. You can't do anything more than that. If your best is good enough, that's great. If not, then it's just too good from the other person. I will come back not only once but more times."
Clijsters saved four match points in her victory over 2011 French Open champion Li and the Belgian looked as if she might be set for another struggle after letting a 5-2 lead slip in the second set.
But the three-time U.S. Open winner rallied to take control of the tie break and advance to her seventh Australian Open semifinal as she beat a No. 1 for the first time in a grand slam.
Having taken more than two years to win her first major title after first reaching the top of the world rankings, the current world No. 14 can sympathize with Wozniacki's plight.
"She's worked very hard to get to where she is, and she's one of the most consistent players. People are almost in a way almost blaming her for it. I think that's something that is really absurd," Clijsters said.
"I think it's all a matter of experience and improving, definitely improving and trying to learn from losses and become better every slam. Then she will definitely get there."
Eleventh seed Clijsters said she had gone to great lengths to ensure her ankle was ready.
"Instead of really focusing on the match you're focusing on trying to get the ankle as good as possible," the 28-year-old said.
"Laying on the couch, every 20 minutes ice, 20 minutes off, 20 minutes ice, 20 minutes off. Leg elevated. Lymphatic drainage, all that stuff.
"I had a light hit yesterday without really sidewards movement, just trying to get a feel for the ball, and then back to the icing and all that same routine all over again."
Azarenka earlier came from behind against Polish eighth seed Agnieszka Radwanska before winning 6-7 (0-7) 6-0 6-2.
It was the 22-year-old's 18th victory in her last 21 matches.
"It was very important to see how I could adjust after not playing really well in the first set," said the Belorussian, whose only previous grand slam semifinal came at Wimbledon last year.
"I completely turned it around, so I'm really, really happy about that. Maybe two years ago I would be like, 'Okay it's not working today.'
"But today I really tried to forget about the first set and start from zero and really fight hard, take it one at a time and keep going."
Wednesday's quarterfinals pit the Czech Republic's Kvitova against Italian world No. 48 Sara Errani and 2008 champion Sharapova against 56th-ranked Makarova -- who beat five-time Australian Open winner Serena Williams in the fourth round.