Novak Djokovic of Serbia in action against David Goffin of Belgium during a semifinal round match at the Miami Open tennis tournament on Key Biscayne, Miami, Florida, USA, 01 April 2016. EPA/ERIK S. LESSER

Novak Djokovic of Serbia in action against David Goffin of Belgium during a semifinal round match at the Miami Open tennis tournament on Key Biscayne, Miami, Florida, USA, 01 April 2016. Djokovic defeated Goffin and will face either Kei Nishikori of Japan or Nick Kyrgios of Australia in the men’s singles final. EPA/ERIK S. LESSER

Dusan Vemic, a coach for Novak Djokovic of Serbia, watches introductions before Djokovic plays against David Goffin of Belgium during a semifinal round match at the Miami Open tennis tournament on Key Biscayne, Miami, Florida, USA, 01 April 2016. Djokovic defeated Goffin and will face either Kei Nishikori of Japan or Nick Kyrgios of Australia in the men’s singles final. EPA/ERIK S. LESSER

Novak Djokovic of Serbia in action against Tomas Berdych of the Czech Republic during their quarterfinal match at the Miami Open tennis tournament on Key Biscayne, Miami, Florida, USA, 30 March 2016. EPA/RHONA WISE

Novak Djokovic of Serbia in action against Dominic Thiem of Austria during a fourth round match at the Miami Open tennis tournament on Key Biscayne, Miami, Florida, USA, 29 March 2016. EPA/ERIK S. LESSER