Kim Clijsters battles past Li Na at Australian Open 2012

Clijsters looked in serious trouble when she rolled her ankle at 3-3, 30-30

Kim Clijsters played through the pain of an ankle injury and saved four match points to stun Li Na and book a place in the Australian Open quarter-finals.

The defending champion landed awkwardly at 30-30 in game six of the first set, which Li won before taking a 6-2 lead in the second set tie-break.

But Clijsters fought back to win 4-6 7-6 (8-6) 6-4 and will next play Caroline Wozniacki who beat Jelena Jankovic.

There were also victories for Victoria Azarenka and Agnieszka Radwanska.

They recorded comfortable straight-sets wins to set up a last-eight encounter, but it is Clijsters who will make the headlines.

When asked if this was the best comeback of her career, the Belgian said: "It has to be. I can't believe I won.

"I knew before the match it would be tough, physically and mentally. But I didn't expect this. It's amazing to get through and fight.

"It was not my best tennis [after the injury] but I just tried to win each point and not give up."

After rolling her left ankle, Clijsters immediately called for the trainer and had it heavily strapped while receiving anti-inflammatory tablets.

The 28-year-old was in considerable pain and, having stated her desire to retire at the end of 2012, it looked like Clijsters had played her last point at Melbourne Park.

"A couple of times it went through my mind [to pull out]," stated the four-time Grand Slam champion.

"But I thought, 'I don't want to quit on my last time at the Australian Open'.

"I just kept fighting. Everyone in my support box was cheering me on and the crowd were amazing, thank you very much. I'm very happy."

Li broke a hobbling Clijsters for 5-4 and comfortably served out the opening set before dominating the second set tie-break.

But at 6-2 down Clijsters went for broke and Li began to crumble. On the fifth seed's final match point, Clijsters played a high-risk drop shot that Li retrieved, but she could not return the subsequent lob.

The crowd were now willing Clijsters on and, after levelling the match, the 11th seed took control of the deciding set. She went two breaks to the good and, although Li clawed one back, Clijsters served out to scenes of jubilation.

Clijsters's quarter-final opponent, world number one Wozniacki, who has yet to win a Grand Slam title, survived a fightback from former world number one Jankovic of Serbia to progress 6-0 7-5.

The Dane has yet to drop a set in this year's tournament and looked to be cruising when she took the first set to love as Jankovic struggled to keep the ball in play.

Wozniacki raced to a 4-1 lead in the second and though Jankovic, who hit 50 unforced errors in the match, levelled the set at 5-5, the Dane broke back and then held her nerve to win on her second match point.

"My confidence is high, my fitness is good, I feel like my play is improving so I'm very positive," said Wozniacki who will play in her second consecutive quarter-final in Melbourne.

"I thought I played a great set and a half and then she started playing very well and got me back on my toes for a bit.

"I'm so happy to be through and even though I know some of the crowd wanted a long match, I hope you will still support me."

Wozniacki is still searching for her maiden Grand Slam title

The first player to advance on day seven was Belarusian third seed Azarenka, who beat Iveta Benesova 6-2 6-2.

She dominated her Czech opponent in every area and again showed why she is a strong contender for the title.

"I felt really good," said Azarenka, who has dropped just 12 games in the tournament. "She's good at shot-making but I was ready for that.

"I had to stay determined throughout. I'm glad I could stay strong and finish it, as sometimes you never know with these players.

"I worked really hard with my team pre-season and then really hard here in Australia. A lot of things are coming together and I try to get better every day."

Depending on results, Azarenka could replace Wozniacki as world number one at the end of the fortnight.

"I'd be a liar if I said I don't care about it," Azarenka added. "It's a bit in the back of my head but I take it day by day and we'll see in one week."

Before that, Azarenka must focus on an in-form Radwanska.

The eighth seed needed just 54 minutes to see off German 22nd seed Julia Goerges, who made 27 unforced errors to her opponent's three.

Radwanska took three hours to overcome Bethanie Mattek-Sands in the opening round but has since dropped only 10 games.

"This was my first match in the Hisense Arena but since the beginning I felt great; everything worked," she said.

"I've known Azarenka for a long time and I will have to play my best tennis to beat her. She's a great champion - it will be tough."