Australian Open - - Serena Advnces While Venus Stumbles; As Quarter Finals Bring Different Luck for William Sisters

MELBOURNE — Serena Williams dug herself out of a hole while big sister Venus put herself in one during an eventful Australian Open women's quarter-finals on Wednesday.

Defending champion Serena was teetering on the brink of an early departure when she trailed Belarus's Victoria Azarenka 4-6, 0-4.

The world number one was struggling to match the power and aggression of the 20-year-old from Minsk, who also had Serena on the ropes in the fourth round in 2009 before retiring with illness.

But Serena showed all her renowned fighting qualities as she came out swinging, winning 12 of the next 16 games to somehow overhaul Azarenka 4-6, 7-6 (7/4), 6-2.

She next plays Chinese 16th seed Li Na, who performed a similar escape act against Venus in the first match on Rod Laver Arena.

The imposing Venus blitzed her way through the first set and led 5-3 in the second before imploding under an avalanche of unforced errors, virtually handing the match to the gritty Li 2-6, 7-6 (7/4), 7-5.

Serena said she surprised even herself with her fightback.

"I didn't expect to win when I was down 0-4 -- I was like 'well at least I am still in the doubles'," she said.

"But I never really count myself out."

With her left knee and right thigh heavily bandaged, Williams was run all around the court by Azarenka.

At 0-4 in the second set, and having not won a point on the Azarenka serve in the set until then, Williams cut a dejected figure and seemed only moments from elimination.

However, she started to swing freely and all the sudden her game returned to its dominant best.

"I knew if I could just do a little better and make a little less errors -- I made a lot -- I knew I could be better," Serena said.

Azarenka was still playing well, but had no answer to the power surge, with Williams hitting 57 winners to her 22.

Meanwhile Li, who joined countrywoman Zheng Jie in the semi-finals, was ecstatic after her two hours, 45 minute win.

"It's the best day of my whole life," she said.

"It's good for both players and it's good for Chinese tennis."

Li and Venus made 110 unforced errors between them in a poor quality match that will be best remembered for the drama of the fluctuating third set, which featured nine breaks of serve.

Li started nervously and seemed overwhelmed by the occasion as she wilted badly in the first set against the power of the American.

She lost the first set in just 30 minutes and was in real trouble when Venus was serving for the match at 5-3 in the second.

But Li began to swing freely and Venus tightened up, losing her serve, then the set in a tiebreak.

"Actually I was nervous in the first set, I mean, Venus played aggressively in the first set," Li said.

"She didn't miss a lot of balls. I was feeling more pressure in the first set. Then in the second set I was feeling a little bit better, but still was like 5-3 down. Then I just tried to get more balls back."

Li's tiebreak win signalled the start of a see-sawing final set in which both players struggled to hold serve -- at one stage there were six consecutive breaks.

Li finally held and came out to serve for the match, only to be broken, but Williams dropped her serve straight away, giving Li another chance.

This time she made no mistake as another unforced error from the American gave her the match.