NEW YORK -- One day after the biggest win of Juan Martin del Potro's career, the 20-year-old Argentine managed to one-up himself.

With a shocking 3-6, 7-6(5), 4-6, 7-6(4), 6-2 victory Monday night, del Potro snapped Roger Federer's streak of five straight U.S. Open titles in dramatic fashion.

Federer, who had lost just one match since April, was trying to become the first man to win six consecutive American championships since Bill Tilden in 1920-25. The top-ranked Swiss had won 40 consecutive matches here, dating back to a semifinal loss to David Nalbandian in 2003.

But with a thunderous serve and punishing forehand, the 6-foot-6 del Potro pounded both streaks into history.

Having upset third-ranked Rafael Nadal in straight sets in Sunday's semifinal, Del Potro became the first player to defeat both Federer and Nadal -- the era's two most decorated players -- in the same Grand Slam tournament.

"It's difficult to explain this moment," del Potro said. "It's my dream."

Del Potro had never defeated Federer in six previous meetings. But he'd shown signs of progress in their most recent clash, a five-set defeat in the French Open semifinals.

Playing in his first Grand Slam final, del Potro confessed to having trouble sleeping because of his nerves. The tension was evident in the first set, as the young Argentine appeared overmatched while struggling to establish his serve and his forehand.

With Federer serving at 5-4, 30-30 in the second set and threatening to stake a two-sets-to-none lead, del Potro struck a booming passing shot that was called out. The call was overturned by the Hawk-Eye instant-replay system, despite objections from Federer, who glared at the chair umpire while pointing at the spot where the ball landed.

On the next point after play resumed, del Potro lined a forehand winner past Federer for his first service break of the match.

"When I broke his serve for the first time, I started to believe in my game," del Potro said.

Federer, a longtime skeptic of electronic line calling, seemed rattled by the sequence.

"I had him under control for the first two sets. I should have never lost so many chances," Federer said. "If I win the second set, I'm in a great position to come through. Unfortunately, I didn't."

The top-seeded Swiss struggled during the third set and fell behind a break, but came back to win the set when del Potro was broken in back-to-back service games.

But de Potro persisted. After winning a fourth-set tiebreak to force a fifth and deciding set, the big-serving Argentine elevated his game just as Federer began to unravel.

Del Potro sprinted out to a three-games-to-none lead and never looked back. Serving at 2-5, 15-40, Federer was able to save a pair of championship points. But the Swiss gave del Potro a third following a double fault -- his 11th of the match.

When Federer's backhand slice landed past the baseline, del Potro fell onto his back and covered his face with his hands.

"Many things came to my mind," del Potro said. "I don't know how I can explain, because it's my dream. My dream is done. It's over. I will go home with a trophy and it's my best sensation ever in my life."

At four hours and six minutes, Monday's match was the second-longest final in U.S. Open history after John McEnroe's classic five-set victory over Bjorn Borg in 1980.

Del Potro became just the second South American champion in the tournament's 118-year-old history after Guillermo Vilas, who won in 1977 when the tournament was played on clay.

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