Seeded sixth at the 2009 US Open, del Potro began by defeating Juan Mónaco and Jürgen Melzer in straight sets, before dropping a set but defeating Köllerer to reach the fourth round. He defeated a resurgent Juan Carlos Ferrero to advance to the quarterfinals for the second consecutive year. Del Potro then advanced to the semifinals by defeating Marin Čilić. Del Potro was down a set and a break, before winning 17 of the final 20 games to win the match. His advance to the semifinals ensured his return to the top 5 in the rankings. He then easily defeated and crushed world No. 3 and reigning Australian Open champion Rafael Nadal in the semifinals to reach his first Grand Slam final. This was his third consecutive victory over Nadal and made him the first Argentine to reach a Grand Slam singles final since Mariano Puerta at the 2005 French Open. In the finals, del Potro rallied from a set and a break down to defeat world No. 1 and five-time defending champion Roger Federer in five sets; his first victory over Federer after six previous defeats, and Federer's first loss in the US Open since 2003. Del Potro stated, "Since was young, I dream with this and take trophy with me", said del Potro, who became the first Argentine male to win the title since Guillermo Vilas in 1977. "I did my dream, and it's unbelievable moment. It's amazing match, amazing people. Everything is perfect." After the match, Federer praised del Potro; "I thought he hung in there and gave himself chances and, in the end, was the better man."