Lion-heart Clijsters overcomes Li Na challenge

Kim Clijsters was courage personified as the defending champion shook off a painful ankle injury and saved four match points to overhaul China's Li Na 4-6, 7-6, 6-4 and reach the quarter-finals of the Australian Open on Sunday.

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The big-hearted Belgian rolled her left ankle at 3-3 in the first set on a scorching day at Rod Laver Arena but rejoined the battle after a lengthy medical time-out with her foot thickly taped.

In a rematch of last year's finalists, 11th seed Clijsters stared at the abyss when 6-2 down in the second set tiebreak but reeled off six points in a row to take the set and spark a rapturous ovation from the stands.

After trailing 4-0 in the decider, the hard-hitting Li recovered to claw back to 5-4 down but Clijsters weathered the challenge to close out the match and keep her hopes alive of a fifth Grand Slam title in her farewell year on tour.

"It has to be (one of my best comebacks)," Clijsters said red-faced in a courtside interview after raising her arms in triumph to acknowledge the roaring crowd. "I can't believe I won.

"I knew before the match that it was going to be a tough match, physically, mentally.

"It was amazing to get through and to fight and probably not with my best tennis."

French Open champion Li took the first set of last year's final against the Belgian but was once again left crestfallen after missing a golden chance to put her Melbourne Park nemesis away.

After saving three match points, Clijsters appeared to suffer a mental lapse on the fourth when she attempted a speculative drop-shot that bounced up and begged to be put away.

Fifth-seeded Li charged in but her attempted winner was equally inept and allowed Clijsters to poke a lob over her head to save the point.

The Chinese subsequently crumbled under the pressure, spraying two backhand shots to lose the set before her serve collapsed as Clijsters charged 5-1 ahead in the decider.

Clijsters will play the winner of top seed Caroline Wozniacki and former World No. 1 Jelena Jankovic who play in the evening session at Rod Laver Arena.

Rafa Nadal was keeping his fingers crossed for the second week of the Australian Open after reaching the quarter-finals with a comfortable 6-4, 6-4, 6-2 win over fellow Spaniard Feliciano Lopez on Sunday.

Since winning his sole title at Melbourne Park in 2009, the 25-year-old has been ushered out of the year's first Grand Slam on the back of injuries at the quarter-final stage.

The second seed arrived this year under another injury cloud and had his left foot strapped by a physiotherapist early in the first set against Lopez on Sunday.

The 10-times grand slam champion still moved nimbly enough to wear down his 30-year-old opponent in searing 35 degree Celcius heat, however, and sealed the match in less than two-and-a-half hours when Lopez looped a service return wide.

Memories of his last eight withdrawal against Andy Murray two years ago and defeat at the hands of David Ferrer last year still clearly haunt him.

"Hopefully it won't happen this time," Nadal said with a smile. "Every year is different. I had a bad experience for the last two years here. It's tough to have to go out of a tournament like Australia in quarter-finals.

"In 2010 I retired because I couldn't continue. Last year I decided not to retire but I had a problem in the second or third game of the match. So I played one complete match with very bad feelings."

Coming off three lop-sided victories, Nadal encountered much stiffer resistance from his Davis Cup team-mate, a fellow left-hander whose chipping and charging to the net had the Mallorcan repeatedly on the back-foot at Rod Laver Arena.

Nadal, who has yet to drop a set at the Australian Open this year, said he was very happy with the way he was playing and that his serve was functioning well.

"I think I started the tournament playing really well this time," said Nadal, who will face Czech seventh seed Tomas Berdych in the last eight.

"Sometimes in a few tournaments I feel that I am improving day by day.

"But now I arrive to quarter-finals. It's the moment to keep playing well and to try to go a little bit more. That's all. In general, I am doing the right things. I am in the right place, at the right moment.

"So now I have to keep playing well and try, if it's possible, to improve a little bit."

Lopez disagreed with his friend in as much as he thought Nadal was improving as well as being, crucially, fully fit.

"He's in a good shape," he told reporters. "If you take the match he played today, I think he's 100 percent physically, which is very important for him.

"I think he's playing better and better every day."

Victoria Azarenka whipped through her match against Iveta Benesova on Sunday to become the first player to reach the Australian Open quarter-finals.

The Belarussian took 77 minutes to dismantle her unseeded Czech opponent 6-2, 6-2 in bright sunshine on Rod Laver Arena and set up a clash against Agnieszka Radwanska or Julia Goerges.

The 22-year-old won the title over a strong field at the Sydney warm-up event last week and has stormed through the first week at MelbournePark with four emphatic victories.

Roger Federer ended the Australian Open hopes of local Bernard Tomic with a 6-4, 6-2, 6-2 victory in the fourth round.

The 30-year-old Federer, who is bidding for his 17th grand slam title, had no room for sentiment for the 19-year-old or the packed crowd on Rod Laver Arena who had been willing the Queenslander to victory.

Federer will now meet Juan Martin Del Potro in the quarter-finals in their first grand slam match up since the Argentine beat the Swiss in the final of the 2009 US Open.

Czech seventh seed Tomas Berdych was booed off Hisense Arena on Sunday after a bad tempered fourth-round victory over Nicolas Almagro at the Australian Open.

Berdych refused to shake hands with the Spaniard after he won the match 4-6, 7-6, 7-6, 7-6, to set up a quarter-final with Rafa Nadal, because he felt the 10th-seeded Almagro had deliberately blasted a return at his head during the fourth set.

The ball rebounded off Berdych's arm and over the net which Amalgro put away for the point, and while the Spaniard apologised immediately, the Czech was still incensed at the conclusion of the three hour, 54 minute match.

Berdych's courtside interview was drowned out by the crowd booing and hissing, while tennis coach Brad Gilbert said he was appalled at the Czech's decision.

"Really poor of the Birdman not to shake hands with Nico," Gilbert wrote on his Twitter page.

"He was way wrong... I am stunned with Tomas."

Caroline Wozniacki saw off a late fightback from former World No. 1 Jelena Jankovic to ease into the quarter-finals of the Australian Open with a 6-0, 7-5 victory.

The top-seeded Dane cruised early but was made to work hard to close out the match in 103 minutes on a balmy evening at Rod Laver Arena.

"My confidence is high, my fitness is good, I feel like my play is improving," Wozniacki beamed in a courtside interview.

"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'll still support me."