Argentine Gaston Gaudio clawed his way back from the brink of defeat to beat Chile's Fernando Gonzalez on Friday, setting up a semi-final with Roger Federer [Images] at the season-ending Masters Cup.

Gaudio saved three match points in a pulsating 1-6, 7-5, 7-5 win and now has the daunting task of halting world number one Federer's charge for a third straight Masters title on Saturday.

Russia's [Images] Nikolay Davydenko plays Argentine David Nalbandian in the other semi-final at the $4.45 million Shanghai tournament.

Davydenko crushed Argentina's Mariano Puerta 6-3, 6-2 to finish top of the Gold Group with a perfect 3-0 record in his first Masters Cup appearance.

"I don't know how I came back," said Gaudio. "I thought I was done. But it gives me a lot of confidence to play Roger tomorrow."

Wimbledon and U.S. Open champion Federer won all three of his Red Group matches to extend his winning streak to 34 matches and his record for the year to 80-3.

Only Ilie Nastase in 1971-73 and Ivan Lendl in 1985-87 have won three in a row at the season-ending extravaganza.

"It is always so difficult and so tough to play Roger," Gaudio told reporters. "But you never know. I think I have a chance."

Gaudio, last year's French Open champion, secured second place in their round-robin group behind Davydenko after digging himself out of a hole to maintain his mastery over Gonzalez.

Gaudio had won all three of his previous meetings with Gonzalez but was in real trouble at a set and 5-3 down and had to fend off three match points in the next game.

CRUCIAL BREAK

Gaudio quickly levelled the match and secured the crucial break in the deciding set on a Gonzalez double-fault to go 6-5 up.

Gaudio's place in the last four was sealed when the hard-hitting Chilean sent a wild forehand well wide after two hours, nine minutes.

The first Chilean to play at the season-ending championship since Marcelo Rios in 1998, Gonzalez cut short his holiday to fly to China as the second alternate.

His chance came when Andre Agassi [Images] pulled out with an ankle injury and Gonzalez promptly beat Puerta, himself a replacement for Rafael Nadal [Images], in his opening match in midweek.

However, he made no excuses after coming up short against Gaudio.

"I absolutely dominated for two sets," he shrugged. "I was feeling the ball unbelievable and hitting shots as I wanted. I tried to go for it but it didn't work this time."

Tournament organisers were frustrated by the sudden withdrawals through injury of Agassi and Nadal earlier this week.

Andy Roddick [Images], Marat Safin [Images] and Lleyton Hewitt [Images] were all Shanghai no-shows.

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