( 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 do n'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 ca n'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 .
Top seed Agnieszka Radwanska loses to Kim Clijsters at the Australian Open . Wozniacki will lose world No . 1 spot and is still searching for a eighth grand slam title . Defending champion Clijsters to face first seed Victoria Azarenka in the semifinals . Belarus ' Agnieszka Radwanska came from one set down to beat eighth seed Azarenka .