Novak Djokovic of Serbia reacts while playing Spain's David Ferrer during a semifinal match at the 2012 US Open tennis tournament,  Sunday, Sept. 9, 2012, in New York. (AP Photo/Mike Groll)

Photo by: Mike Groll

Novak Djokovic of Serbia reacts while playing Spain's David Ferrer during a semifinal match at the 2012 US Open tennis tournament, Sunday, Sept. 9, 2012, in New York. (AP Photo/Mike Groll)