MELBOURNE - Defending champion Kim Clijsters saved four match points as she dug deep to beat China's Li Na in a dramatic fourth round match at the Australian Open on Sunday.

Clijsters, who rolled her ankle midway through the first set and needed medical treatment, came back from 6-2 down in a second set tie-break to defeat a shell-shocked Li 4-6, 7-6 (8/6), 6-4.

It was a magnificent turnaround from the Belgian, who looked down and out as she hobbled to her chair at 3-3 in the first set after hurting her ankle during a baseline rally.

The much-anticipated rematch of last year's final had threatened to turn into a huge anti-climax as Clijsters struggled to continue after the fall.

But her sheer determination enthralled the big crowd in the Rod Laver Arena, who swung their support behind the 28-year-old, making her last tournament appearance in Australia before retiring at the end of 2012.

“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.

Clijsters decided to battle on, but it soon became obvious that she was not moving as well as she normally does and she had trouble chasing down Li's wide balls.

She managed to hold her serve after the injury, coming back from a break point down to save the game, but Li then broke Clijsters' next service game and held her own to take the first set in 43 minutes.

Clijsters fought hard to hold serve at the start of the second set but her lack of movement meant she was always on the defensive and Li took full advantage, holding her own serve then breaking Clijsters.

But the gallant Clijsters began moving better and she broke to get the set back on level terms.

Both players held firm to take the set to a tie-break, where Li opened a 6-2 lead, only for Clijsters to win six points in a row to level the match,

By this point the match had swung firmly back towards Clijsters as Li appeared to collapse mentally, losing her first two service games as the defending champion raced into a 4-0 lead.

Li held her next two service games to make it 5-2, then broke Clijsters as she served for the match for the first time.

The Belgian had a second chance at 5-4 and this time made no mistake, claiming victory when a Li backhand hit the net on her second match point.

“I knew beforehand it was going to be a tough match, physically, mentally, everything,” Clijsters said.

“But I didn't expect this -- it was amazing to get through.”