By Nick Mulvenney

SYDNEY (Reuters) - China's Li Na staged a remarkable comeback from 5-0 down in the first set to upset Australian Open favorite Kim Clijsters 7-6 6-3 in the final of the Sydney International on Friday.

It was a first loss in 14 semi-finals and finals for Clijsters since her return from retirement in August 2009 and the manner of defeat will be a setback to her preparations just three days from the start of the year's first grand slam.

"Obviously I'm disappointed," said the Belgian, the 2003 and 2007 champion at the Sydney Olympic Park.

"But to me personally, I think more about the feeling that I had out on the court ... Today I lost, and the feeling ... wasn't the way I would have liked it to be."

It had taken Clijsters just 18 minutes to rack up a 5-0 lead in the first set with the Belgian's game looking as impressive as it had all week and Li's first serve deserting her.

"I saw the time," said Li. "I was like, 'the fans, they've paid a lot of money and the match will be over in half an hour'.

"I didn't believe I could get back from there but it all just changed in one or two points."

Just 18 minutes further into the contest the score was level at 5-5 and Clijsters was racking up double faults and spraying forehands all over the place.

"I think I just softened the quality of my strokes," said Clijsters. "You know, I wasn't hitting quite as deep as before and not as aggressively, and she definitely took over very quickly."

Clijsters held serve to force a tiebreak, which she then led 3-1 before Li reeled off six points to clinch the set.

Another fluffed forehand saw Clijsters give up her first service game of the second set and the three-times grand slam winner vented her anger by hammering a ball into the ground.

"I wasn't serving great," the 27-year-old added. "You try to fight but then it becomes frustrating that you are not able to play your best when you're trying to."

A glimmer of hope that the Belgian might still be able to rescue the match came with a sublime drop volley that earned her a break back.

By now, though, Li was charged with confidence and her big backhand allowed her to ram home her advantage over Clijsters, who finished the match with seven double faults and 27 unforced errors.

"I look forward to going back out on the practice courts and trying to improve again and to obviously play my first round in Melbourne," said Clijsters, who meets former world No.1 Dinara Safina of Russia in her opener.

(Editing by Martyn Herman)