Melbourne: Belgian iron-woman Kim Clijsters had to ignore voices in her head telling her to give up on her Australian Open title defence when she suffered an ankle injury in her fourth-round match against Li Na on Sunday.

The four-times major champion decided to play on, however, and gritted her teeth until the pain-killers kicked in before riding the emotion of her final appearance at Melbourne Park to victory.

"It definitely crossed my mind at some point," the 28-year-old said after her 4-6 7-6 6-4 victory over fifth seed Li Na.

"But I knew if I could just try to kind of let the medication sink in or if I could get through the first 20 minutes, half hour, I think the pain would go away a little bit and then maybe with the adrenaline I could just fly through it.

"Yeah, I did, and I'm happy that I didn't give up." Clijsters slumped to the ground when her left ankle rolled underneath her as she swiped at a forehand on the baseline at 3-3 in the first set.

She was back on her feet in a flash, though, and played out the point hobbling before heading to her chair for a lengthy medical time-out.

Returning to a huge ovation from the stands at Rod Laver Arena, she worked her way through the pain to take the match to a tiebreak in the second set.

Clijsters showed her formidable mental strength to save four match points to seal the tiebreak and raced to a 4-0 lead in the decider before closing out the match with a tense service game.

She was lucky on the fourth match point, when her Chinese opponent failed to put away an ill-struck drop-shot that was begging to be dispatched.

"I think she was a little bit, you know, lost or maybe a little bit confused at that time, and she made two pretty easy mistakes when we changed sides," Clijsters said with her leg elevated in recovery mode.

"She started making a few easier mistakes, especially in the beginning of that third set where after having those match points I think maybe it got to her a little bit."

Clijsters, who came into the tournament under a cloud from a hip muscle injury, faces either top seed Caroline Wozniacki or former world number one Jelena Jankovic in the quarter-finals.

(Agencies)