Federer seals semi spot in Oz

Down a set and a break in the second, the Swiss top seed turned the match in the blink of an eye, winning 13 consecutive games to take the next two sets and a 2-0 lead in the fourth as Davydenko was left chasing shadows around the Rod Laver Arena.

Sixth-seeded Davydenko rallied, however, breaking serve twice and saving a match point to claw back into contention, but was broken again at 5-5, allowing Federer to calmly serve out the match and seal it with a forehand winner.

Federer, beaten by Rafa Nadal in the last year's final, has now reached 23 successive grand slam semi-finals since being knocked out of the third round of the French Open in 2004.

Serena Williams summoned all her fighting qualities to beat Victoria Azarenka 4-6 7-6 6-2 today after her sister, Venus, crashed out of the tournament.

Li Na stunned Venus earlier in the day to become the second ever Chinese to reach a grand slam semi-final.

Serena showed why she remains the toughest woman in the world to beat, however, 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 tomorrow's semi, while Li faces the daunting prospect of playing Serena.

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 and then went 4-0 behind in the second as she started to doubt herself.

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