FILE - In this Friday March 23, 2012 file photo, Kei Nishikori of Japan serves to Lukas Lacko of Slovakia during the Sony Ericsson Open tennis tournament in Key Biscayne, Fla.. Japanese tennis star Kei Nishikori has enlisted the help of Michael Chang as he looks to break into the top 10 in 2014. Chang will join Nishikori's coaching staff for 17-20 weeks in 2014, Nishikori's management team announced on Wednesday Dec. 11, 2013. (AP Photo/Lynne Sladky, File)