Marin Cilic kisses the championship trophy after defeating Kei Nishikori in the championship match of the U.S. Open Monday in New York.

Marin Cilic of Croatia celebrates after defeating Kei Nishikori of Japan in the championship match of the U.S. Open on Monday in New York.

Arthur Ashe Stadium fills up with spectators for the championship match of the 2014 U.S. Open tennis tournament between Serena Williams, of the United States, and Caroline Wozniacki, of Denmark, Sunday.

Kei Nishikori, of Japan, follows through on a shot as his coach Michael Chang looks on during a practice session before the championship match against Marin Cilic, of Croatia, at the 2014 U.S. Open tennis tournament, Monday.

Marin Cilic, of Croatia, reacts after a shot against Roger Federer, of Switzerland, during the semifinals of the 2014 U.S. Open tennis tournament, Saturday.