Serena survives after Venus falls to Li Na

Li Na earlier stunned Venus to become just the second Chinese to reach the semi-finals of a Grand Slam.

Serena showed why she remains the toughest woman in the world to beat, battling back from the brink of defeat to remain on course to defend the title she won for the fourth time last year.

Her elder sibling might have joined her but threw away a match-winning lead in her 2-6, 7-6, 7-5 loss to Li, one of two Chinese through to the last four in Melbourne.

Venus was two points away from winning the match in the second set when she stumbled on her serve and allowed Li back into the contest.

"In tennis you have to close it out. It's not like there's a clock ticking and then suddenly it's over," Venus said.

"You just have to close it out. I didn't do that today."

The once unimaginable prospect of an all-Chinese final is suddenly looming as a real possibility after Li followed Zheng Jie into the semis.

Zheng beat Maria Kirilenko 24 hours earlier and plays Justine Henin in Thursday's semis while Li faces the daunting prospect of playing Serena.

CHINESE PHILOSOPHY

Millions of people in China have been following their matches on television and Li said she was adopting a philosophical approach to her match against Serena.

"In China we say if you have a tough time and then you return back, maybe you have good luck for after," she said. "So I still believe that."

Serena's title defence was hanging by a thread after she lost the opening set to Azarenka then went behind 4-0 in the second as she started to doubt herself.

But, as she has done so many times in the past, Serena was able to raise her game when she needed to and found a way to win.

"I'm surprised. I didn't expect to win when I was down in the second set," said Serena, who remains a strong favourite for the title.

"I thought if I lost the singles and the doubles, I could catch a flight on Friday -- it's not what a champion is supposed to think but I did."