Roger Federer [Images] survived his toughest test to reach the U.S. Open semi-finals on Thursday, coming through two pressure-packed tiebreaks to beat a stubborn James Blake 7-6, 6-0, 6-7, 6-4.

The world number one took the first set in a tiebreak and lost the third on another before reaching his 10th successive grand slam semi-final to match Ivan Lendl's record Open era streak.

"I thought it was a fantastic match," the top seed and twice defending champion told reporters. "Unbelievable, high quality. I really thought we were hitting the ball so hard.

"I thought it was a great match and I thought James had a lot to do with it, actually."

The fifth-seed Blake was happy to have made the Wimbledon and Australian Open champion work hard for his victory.

"It wasn't just a walk in the park for him, I'd like to think," the American said. "I definitely feel like I let him know that I can play."

Federer will meet seventh seed Nikolay Davydenko on Saturday for a place in the final following the Russian's five-set victory over Germany's [Images] Tommy Haas. The Swiss has won all seven of their previous meetings.

The other semi-final pits American ninth seed Andy Roddick [Images], the 2003 champion, against unseeded Russian Mikhail Youzhny.

After winning the opening tiebreaker 9-7, saving three set points held by Blake, Federer looked poised to make the American his fifth successive straight-sets victim as he cruised through the second in only 22 minutes.

HARD-FOUGHT WIN

"That's just an old fashioned whuppin' in the second set," Blake said.

Blake, driven on by a boisterous home support, battled back from a break down early in the third set but looked beaten when he lost serve to trail 5-3 with Federer serving for the match.

A sizzling forehand crosscourt winner in the next game got the break back, however, and Blake sent the match to another tiebreak.

"To a certain extent I take pride in the way that I fought," said Blake, who had failed to win a set against Federer in four previous meetings.

Federer saved four set points and held match point at 9-8 but Blake produced a backhand winner down the line and took the next two points to force a fourth set.

The Swiss again looked set to sail to victory, going up by two breaks for a 5-1 lead before Blake hit back with a break of his own.

Federer finally saw off Blake on his third match point of the 10th game when the American dumped a backhand into the net after some spirited baseline rallies.

Federer said there was no question it was his hardest test at the season's last grand slam.

"I think the score says it all," he said. "We both missed our opportunities here and there because we took so many chances on our shots and it turned out to be a thriller, really."

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