MELBOURNE, Australia - With the possibility of it being the last Australian Open match of her career Kim Clijsters left it all on the court, pulling off a miracle comeback from quadruple match point to beat Li Na, 46 76(6) 64.

Although Clijsters had won five of her seven previous meetings with Li, it didn't look like her day at all early on in the match, rolling her ankle at 3-all in the first set and continuing to play through some suspect movement, at best. She lost the first set and trailed 3-1 in the second set, but she never stopped fighting. "It probably wasn't my best tennis, but you fight on every shot and try to win each point," she said. "You never know what will happen on the other side of the net."

Leading 6-2 in the second set tie-break, Li gave up the first two match points with forehand errors; Clijsters hit a forehand winner to save the third, then on the fourth - after a long exchange from the baseline - she hit a drop shot, which Li got to, but the Belgian lobbed her. Two points later Clijsters had the set.

Clijsters carried that momentum to a 5-1 lead in the third set, and although Li caught up to 5-4 and even fended off a match point herself, the Belgian kept her cool and closed out the thriller on one last Li backhand into the net.

"I can't believe I won," Clijsters said afterwards. "It crossed my mind a couple of times to stop because of the ankle, but it's my last time at the Australian Open and I didn't want to quit in my last match. My box and the crowd were cheering me on as well and I just tried to keep fighting and get back into it.

"I knew it would be tough but I didn't expect this. It was amazing."

Interestingly, Clijsters was actually the on-paper underdog in the match - after missing much of 2011 with a variety of injuries her ranking has fallen and she is the No.11 seed here, while Li was the No.5 seed. It was the earliest Grand Slam final rematch at that same Grand Slam the next year in the Open Era.

Clijsters was the third woman into the quarterfinals. Earlier in the day, Victoria Azarenka and Agnieszka Radwanska both cruised through, No.3-seeded Azarenka beating Iveta Benesova, 62 62, and No.8-seeded Radwanska having it even easier in a rout against No.22 seed Julia Goerges, 61 61.

Goerges was playing the fourth round of a Grand Slam for the first time, but went awry, hitting 27 errors to just 11 winners - the rock solid Radwanska had 10 winners but an amazing three unforced errors. "It was one of those days where nothing worked. No balls went in," Goerges said. "She made I think two unforced errors in two sets. It's pretty tough when you go for your shots and miss them most of the time - almost all. It was a tough day for me."

Azarenka and Radwanska, good friends, will be playing each other for the 10th time, with Azarenka leading their head-to-head series, 6-3. The Belarusian has also won four of their last five meetings - but they've all been close.

"We've had so many great matches, long matches, long rallies. I'm sure it's going to happen again," Azarenka said. "I think she has improved tremendously since the end of last year. You can see the difference. She became more aggressive and improved her serve. It's going to be a really tough battle. She's a very difficult player to play against. But I'm going to try my best."

"I've known Vika for 10 years, I think. We played juniors together. We're the same age, so we've played against each other a lot," Radwanska said. "It's always three sets, always tough ones. I have to play my 100% to beat her."

While Azarenka is going for her second Grand Slam semifinal - she went that far at Wimbledon last year - Radwanska is going for her very first. "I did some quarterfinals, but that's why I'm going to do my 100% this time, to be in the semifinals for the first time," she declared. "But it's not going to be easy - everybody is playing very well, every day, so we'll see what happens."