Kim Clijsters tried her best to hide the pain she was feeling after her Australian Open semi-final loss to Serena Williams on Thursday.

The Belgian flashed one of her famous bright smiles and even tried to crack a joke, but there was no way she could conceal the fact she had just become a victim of the nervous condition all top athletes dread, the "choke".

"I was so close to beating her," a stunned Clijsters said after squandering two match-points and a 5-1 lead in the third set to slump to a 4-6, 6-3, 7-5 defeat.

"It's disappointing but I just have to try and keep my chin up."

The 19-year-old had looked to be cruising towards her second grand slam final as she tormented the world's best female player to open up a seemingly unbeatable lead in the deciding set. But suddenly and inexplicably, she fell apart at the seams.

Sensing her chance, Williams rattled off six straight games to book her place in the final, condemning Clijsters to the tag of being a choker.

Clijsters's desperate collapse immediately brought back memories of two of tennis' other great female chokers.

Jana Novotna lost the 1993 Wimbledon final to Steffi Graf after she got to within a point of leading 5-1 in the third set.

Martina Hingis lost last year's Australian Open final to Jennifer Capriati after she won the first set, led 4-0 in the second then blew four match-points before losing in the third.

Clijsters knew she had her chances. She missed two match-points on Williams's serve in the eighth game of the final set.

She failed to serve out the match at the first opportunity when she led 5-2 then failed again at 5-4 when she started with consecutive double-faults.

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Clijsters, one of the most popular and gracious players in the women's tennis, refused to accept she had choked, saying Williams should be given all the credit for the way she fought back.

"I can't blame myself for anything, you know," Clijsters said.

"I just kept trying to hang in there but it just wasn't good enough at the end.

"I wasn't nervous at all, I think she just started hitting winners.

"If she plays her best, it's very hard to beat her."

Clijsters went into the match as the outsider but still brimming with confidence after beating the powerfully built American at last year's season-ending WTA Championships.

She had won 24 of her last 25 matches before her encounter with Williams and had not dropped a set in reaching the semi-finals.

She seemed to have Williams's measure as she matched her stroke for stroke through the first two sets then raced away in the third when she suddenly caved in.

"Out of every match you win or lose, you learn something," she said.

"She hit some really good returns and everything. That's why she's number one, she can step it up.

"She was just so much more aggressive. The only thing I think I could have made some more first serves and just try and get a little bit of an advantage from the beginning of the point.

"I was close, really close, to winning that. But even on match point she just came up with a shot that was too good."