NEW YORK, NY - SEPTEMBER 09: Rafael Nadal of Spain poses with the US Open Championship trophy as he celebrates winning the men's singles final match against Novak Djokovic of Serbia on Day Fifteen of the 2013 US Open at the USTA Billie Jean King National Tennis Center on September 9, 2013 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Matthew Stockman/Getty Images) (2013 Getty Images)
Rafael Nadal, of Spain, holds up the championship trophy after winning the men's singles final over Novak Djokovic, of Serbia, at the 2013 U.S. Open tennis tournament, Monday, Sept. 9, 2013, in New York. (AP Photo/Darron Cummings) (THE ASSOCIATED PRESS2013)
NEW YORK, NY - SEPTEMBER 09: Rafael Nadal of Spain poses with the US Open Championship trophy after winning the men's singles final match against Novak Djokovic of Serbia on Day Fifteen of the 2013 US Open at the USTA Billie Jean King National Tennis Center on September 9, 2013 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Mike Stobe/Getty Images for the USTA) (2013 Getty Images)
Novak Djokovic, of Serbia, and Rafael Nadal, of Spain, pose for photos after Nadal won the men's singles final of the 2013 U.S. Open tennis tournament, Monday, Sept. 9, 2013, in New York. (AP Photo/David Goldman) (AP2013)
NEW YORK, NY - SEPTEMBER 09: Rafael Nadal of Spain bites the US Open Championship trophy as he celebrates winning the men's singles final match against Novak Djokovic of Serbia on Day Fifteen of the 2013 US Open at the USTA Billie Jean King National Tennis Center on September 9, 2013 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Elsa/Getty Images) (2013 Getty Images)
NEW YORK, NY - SEPTEMBER 09: Rafael Nadal of Spain celebrates winning the men's singles final match against Novak Djokovic of Serbia on Day Fifteen of the 2013 US Open at the USTA Billie Jean King National Tennis Center on September 9, 2013 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Chris Trotman/Getty Images for the USTA) (2013 Getty Images)
Rafael Nadal, of Spain, reacts after defeating Novak Djokovic, of Serbia, during the men's singles final of the 2013 U.S. Open tennis tournament, Monday, Sept. 9, 2013, in New York. (AP Photo/Peter Morgan) (AP2013)
NEW YORK, NY - SEPTEMBER 09: Rafael Nadal of Spain reacts during his men's singles final match against Novak Djokovic of Serbia on Day Fifteen of the 2013 US Open at the USTA Billie Jean King National Tennis Center on September 9, 2013 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Mike Stobe/Getty Images for the USTA) (2013 Getty Images)
NEW YORK, NY - SEPTEMBER 09: Rafael Nadal of Spain celebrates winning the men's singles final match against Novak Djokovic of Serbia on Day Fifteen of the 2013 US Open at the USTA Billie Jean King National Tennis Center on September 9, 2013 in the Flushing neighborhood of the Queens borough of New York City. (Photo by Jaime L. Mikle/Getty Images for the USTA) (2013 Getty Images)