Aged thirteen, Novak Djokovic appeared at coach Nikola Pilic's tennis academy near Munich. He would soon become Pilic's star pupil thanks to his incredible self-discipline and natural tennis brain. Twenty grand slams later, the Serbian star is still in touch with Nikola Pilic, and regards him as one of his mentors. Nikola Pilic speaks to Petra Zivic.

PHOTO: Novak Djokovic in 2008, the year he won his first tennis major (Getty Images)