The 2009 US Open was a tennis tournament played on outdoor hard courts, held from August 31 to September 14, 2009, in the USTA Billie Jean King National Tennis Center at Flushing Meadows, New York City, United States. Originally, it was scheduled to end with the men's singles final match on Sunday, September 13, but due to rain the tournament was extended by one day. Like the Australian Open, the tournament featured night matches. In the men's singles final, five-time defending champion Roger Federer lost to Argentina's Juan Martín del Potro in a match lasting over four hours.