Melbourne, Jan 27 (DPA) Roger Federer, troubled by the setting sun, held his nerve for a dramatic 2-6, 6-3, 6-0, 7-5 turnaround victory and a semi-final place over Nikolay Davydenko at the Australian Open here Wednesday.

The Swiss top seed trailed 2-6, 1-3 as the Russian who had won their last two matches had his way early in the contest.

But a strategic toilet break after dropping the first set may have helped in the Swiss salvation, with Federer taking his time in hopes that the sun would move down the horizon just that extra little bit.

“Maybe it would set by one or three centimetres,” joked the world number one who has now reached a record 23 straight Grand Slam semi-finals. “I struggled with the sun on the side and with him playing so well.

“It was like a rain delay, you hang on and hope.”

Federer kicked into top gear in the nick of time, his mighty game coming to the fore on the way to a 13-2 record against the Russian who ended last season by taking the year-end championships and began this one with a title in Doha.

“I’ve played him many times, he goes through phases,” said Federer, whose top ranking would have been under threat from Novak Djokovic had he lost. “He can play rock-solid but also a notch below.

“I had to stay positive. I’m surprised I played that great. I’m happy to beat a player like him.”

Federer served for the match in the fourth set leading 5-4 only to be knocked by the Russian sixth seed.

“He gave me three winners, three screamers,” said Federer. “I was thinking ‘why did you do that, just one in the net and we’re done here’.

“There was a bit of luck involved for me. But I also played very well,” said the Swiss, who struck 43 winners and broke on eight of 14 occasions.

Djokovic was playing a re-run of the 2008 final against Frenchman Jo-Wilfried Tsonga later Wednesday.

Women’s top seed Serena Williams saved the day from a looming family disaster, posting a comeback quarter-final to avenge the defeat of her sister Venus.

The invincible reputation of the seeded US pair took a hit when number six Venus was humbled by Li Na 2-6, 7-6 (7-4), 7-5.

China’s Li made history by joining compatriot Jie Zheng in the semi-finals, making ite first time that two Chinese have done so in a Grand Slam. Li next plays former number one Justine Henin.

Serena also looked to be in desperate straits, down a set and 4-0 against seventh seed Azarenka. But the Belarusian let her momentum slip, with number one Williams scratching to 4-6, 7-6 (7-4), 6-2 survival.

The top seed admitted that she had her mind on what looked to be an upcoming plane trip home before rallying.

“I’m surprised, I didn’t expect to win being down 0-4. I was thinking that if I went out in doubles, that I could catch a flight on Friday. But I’m just happy to still be here,” she said.

Five-time Wimbledon champion Venus cracked under pressure against Li after serving early on for a comfortable straight-set victory, allowing the 16th seed to begin a grinding comeback.

Li broke Venus Williams four times in the third set as the American’s unforced error count raced past 50.

“This is the best day of my whole life,” said Li, who was two points from defeat at one stage and is to become the first Chinese ever to rank in the top 10 in Monday’s rankings.

“I lost the first set, but my coach tells me never to give up,” she said of Swede Thomas Hogstedt. “This is good for both of us and for China tennis.

“In the second set I was feeling a little bit better,” Li said. “But was 5-3 down. Then I just tried to play more ball back. I had chances and I was able to do it.”