LOS ANGELES, CA - DECEMBER 13: Kei Nishikori and Jack Sock meet prior to their match at the Maria Sharapova and Friends, presented by Porsche exhibition on December 13, 2015 in Los Angeles, California. (Photo by Joe Scarnici/Getty Images for IMG)
LOS ANGELES, CA - DECEMBER 13: Kei Nishikori and Jack Sock meet prior to their match at the Maria Sharapova and Friends, presented by Porsche exhibition on December 13, 2015 in Los Angeles, California. (Photo by Joe Scarnici/Getty Images for IMG)