Novak Djokovic of Serbia arrives for his tennis match against Stan Wawrinka

Djokovic of Serbia arrives for his tennis match against Wawrinka of Switzerland at the ATP World Tour finals at the O2 Arena in London

Novak Djokovic of Serbia arrives for his tennis match against Stan Wawrinka of Switzerland at the ATP World Tour finals at the O2 Arena in London.

Marin Cilic of Croatia defeated Kei Nishikori of Japan in their men’s singles final

Cilic of Croatia kisses his trophy after defeating Nishikori of Japan in their men's singles final match at the 2014 U.S. Open tennis tournament in New York

Marin Cilic of Croatia kisses his trophy after he defeated Kei Nishikori of Japan in their men’s singles final match at the 2014 U.S. Open tennis tournament in New York.