Fans watch as Novak Djokovic of Serbia celebrates after defeating Kei Nishikori of Japan during the men’s singles final match at the Miami Open tennis tournament on Key Biscayne, Miami, Florida, USA, 03 April 2016. EPA/ERIK S. LESSER

Kei Nishikori of Japan reacts against Novak Djokovic of Serbia during the men’s singles final match at the Miami Open tennis tournament on Key Biscayne, Miami, Florida, USA, 03 April 2016. Nishikori lost to Djokovic. EPA/ERIK S. LESSER

Victoria Azarenka of Belarus in action against Svetlana Kuznetsova of Russia during the women’s singles final match at the Miami Open tennis tournament on Key Biscayne, Miami, Florida, USA, 02 April 2016. Azarenka defeated Kuznetsova. EPA/ERIK S. LESSER

A multiple exposure picture shows Kei Nishikori of Japan in action against Nick Kyrgios of Australia during their semifinal round match at the Miami Open tennis tournament on Key Biscayne, Miami, Florida, USA, 01 April 2016. EPA/ERIK S. LESSER

Kirsten Flipkens of Belgium returns the ball to Andreea Mitu of Romania during their second round match at the WTA Katowice Open tennis tournament in Katowice, Poland, 06 April 2016. EPA/ANDRZEJ GRYGIEL