2009 US Open – Men's singles

Juan Martín del Potro defeated the five-time defending champion Roger Federer in the final, 3–6, 7–6(7–5), 4–6, 7–6(7–4), 6–2 to win the men's singles tennis title at the 2009 US Open. It was his first (and only) major title. He became the first Argentine man to win the title since Guillermo Vilas in 1977, and the first to win a major since Gastón Gaudio in the 2004 French Open. This was also the first US Open final since 1999 to go to five sets.

Federer was attempting to become the first man to win six consecutive US Open titles in the Open Era, and the first since Bill Tilden in 1925. He was also vying to become the first man to win the Surface Slam (winning majors on clay, grass and hard court in the same calendar year), having won the preceding French Open and Wimbledon. It was the only major not won by the Big Four between the 2005 Australian Open and the 2014 Australian Open, a span of 35 events. This is the only major where Novak Djokovic, Federer, and Rafael Nadal all reached the semifinals, but none of them won the championship. It's also the only major not won by the Big Three in a 30 major span, from the 2005 French Open to 2012 Wimbledon.

This was the first major since the 2006 Australian Open not to have Federer and Nadal as the top two seeds. Andy Murray was seeded second ahead of Nadal, having become the world No. 2 shortly before the tournament. Nadal reclaimed the world No. 2 ranking after Murray lost to Marin Čilić in the fourth round.

This tournament marked the final major appearance of two-time major champion and world No. 1 Marat Safin.

For the first time in US Open history, no Americans reached the quarterfinals.

Seeds
• Roger Federer (final)

• 🇬🇧 Andy Murray (fourth round)

• 🇪🇸 Rafael Nadal (semifinals)

• 🇷🇸 Novak Djokovic (semifinals)

• 🇺🇸 Andy Roddick (third round)

• 🇦🇷 Juan Martín del Potro (champion)

• 🇫🇷 Jo-Wilfried Tsonga (fourth round)

• 🇷🇺 Nikolay Davydenko (fourth round, retired because of a hip injury)

• 🇫🇷 Gilles Simon (third round, retired because of a knee injury)

• 🇪🇸 Fernando Verdasco (quarterfinals)

• Fernando González (quarterfinals)

• 🇸🇪 Robin Söderling (quarterfinals)

• 🇫🇷 Gaël Monfils (fourth round)

• 🇪🇸 Tommy Robredo (fourth round)

• 🇨🇿 Radek Štěpánek (fourth round)

•  Marin Čilić (quarterfinals)

• 🇨🇿 Tomáš Berdych (third round)

• 🇪🇸 David Ferrer (second round)

•  Stan Wawrinka (first round)

• 🇩🇪 Tommy Haas (third round)

• 🇺🇸 James Blake (third round)

• 🇺🇸 Sam Querrey (third round)

• 🇩🇪 Philipp Kohlschreiber (third round)

• 🇪🇸 Juan Carlos Ferrero (fourth round)

• 🇺🇸 Mardy Fish (withdrew because of a rib injury)

• 🇫🇷 Paul-Henri Mathieu (first round)

•  Ivo Karlović (first round)

• 🇷🇴 Victor Hănescu (first round)

• 🇷🇺 Igor Andreev (first round)

• 🇷🇸 Viktor Troicki (second round)

• 🇦🇺 Lleyton Hewitt (third round)

• 🇪🇸 Nicolás Almagro (third round)