The youngest men's finalist at Roland Garros since Michael Chang won the title at 17 in 1989, Nadal will play for the championship tomorrow against unseeded Argentine Mariano Puerta, a 6-3, 5-7, 2-6, 6-4, 6-4 winner over Russia's Nikolay Davydenko. It will be the first French men's final between left-handers in the Open era.

"It's incredible to beat Federer," said Nadal, who avenged a five-set loss to him at Key Biscayne, Fla., two months ago, extended his winning streak to 23 matches and moved within one victory of becoming the first player to win the French Open in his debut since Mats Wilander in 1982. "Winning a semifinal is already incredible, and beating Federer is even more amazing."

From the opening point, a stunning forehand pass that whizzed by the top-ranked Federer on his serve, Nadal showed he was neither intimidated by the four-time Grand Slam winner, nor overwhelmed by the occasion. He had won five titles this year, all on clay, and he treated this biggest clay event of all as if he were born to win it.

"I started bad and finished bad," Federer said. "I was good in the middle, but that was not good enough."

They had walked out on court with different demeanors, Nadal unsmiling and intense, Federer relaxed and waving, the crowd giving both an ovation as they settled in for what promised to be the match of the tournament. The fans would not be disappointed.

The players cast long shadows on the brick red clay when they started the match at 6:29 p.m., the sun shining once again after a 1 1/2-hour rain delay before the 3 1/2-hour duel between Puerta and Davydenko.

Mishitting an unusual number of shots, Federer couldn't tame his forehand or make much use of his generally superior serve. He suffered three breaks to lose the first set and saw the end of his streak of 28 straight sets won over the past 11 matches going back to the tuneup in Hamburg.

Puerta, of Argentina, rallied from a 4-2 deficit in the final set to beat Davydenko.

Puerta has climbed to 37th in the rankings from 440th last August. And now, playing in his first major event since serving a nine-month doping suspension, he has reached the first Grand Slam final in his nine-year career.

"I had two years when I was almost out of the circuit," Puerta said. "I can't believe that on Sunday I'm going to play the final of Roland Garros. I don't even know how to explain that."