Clijsters, Nadal reach Australian Open quarter-final January 22, 2012 -- Updated 0830 GMT (1630 HKT) Kim Clijsters turned her ankle during her fourth round women's singles match against China's Li Na. Belgium's Kim Clijsters beat Li Na of China in last year's Melbourne final The former World No.1 was in trouble early on as she turned her ankle Rafael Nadal will play Tomas Berdych in the last 8 after cruising past Feliciano Lopez Argentina's Juan Martin del Potro will play Roger Federer or home favorite Bernard Tomi (CNN) -- Defending champion and 11th seed Kim Clijsters saved four match points as she overcame the opponent she beat in last year's Australian Open final, Li Na, 4-6 7-6 6-4 on Sunday. The former World No.1 was in trouble early on as she turned her ankle in the opening set and needed medical treatment. Fifth seed Li took full advantage of her opponent's discomfort by taking the first set 6-4. However Clijsters showed typical resilience when she leveled the match after a dramatic tie break, during which she faced match point four times. The setback clearly stunned Li, who quickly found herself 5-2 down in the deciding set before staging a late rally. But the momentum was with the Belgian, as she served out the match to earn a place in the quarter-finals in Melbourne. A couple of times it went through my mind (to retire), but I didn't want to quit at my last time at the Australian Open. Kim Clijsters "A couple of times it went through my mind (to retire), but I didn't want to quit at my last time at the Australian Open," she said after the match, in quotes carried by Agence France-Presse. "I knew beforehand it was going to be a tough match, physically, mentally, everything," she added. But I didn't expect this -- it was amazing to get through. Elsewhere Sunday, World No.3 Victoria Azarenka of Belarus cruised past Czech Iveta Benesova 6-2 6-2, to reach the last eight. She will now face Agnieszka Radwanska, after the Pole thrashed Julia Goerges of Germany 6-1 6-1 earlier in the day. On the men's side, World No.2 Rafael Nadal sailed into the sealed a quarter-final spot after beating fellow Spaniard Feliciano Lopez 6-4 6-4 6-2 in a one-sided match. I've started the tournament playing really well this time. I felt I've played well from the first match and today I played another complete match," Nadal told reporters, in quotes carried by AFP. Now I'm in the quarter-finals. I am doing the right things. I am in the right place, right moment. The second seed will next play Tomas Berdych, who beat Nicolas Almagro 4-7 7-6 7-6 7-6. Argentina's Juan Martin del Potro is also through to the quarter-final stage after a straight sets win over German Philipp Kohlschreiber. He will face either Roger Federer or home favorite Bernard Tomic.