Feliciano Lopez of Spain returns to Novak Djokovic of Serbia during their quarter final match of Dubai Duty Free Tennis ATP Championships in Dubai, United Arab Emirates, 25 February 2016. EPA/ALI HAIDER

Roberto Bautista Agut of Spain returns the ball to Marcos Baghdatis of Cyprus during their quarter final match of the Dubai Duty Free Tennis ATP Championships in Dubai, United Arab Emirates, 25 February 2016. EPA/ALI HAIDER

The Centre Court is seen reflected in the sun glasses of a spectator during the quarter final match between Tomas Berdych of the Czech Republic and Nick Kyrgios of Australia at the Dubai Duty Free Tennis ATP Championships in Dubai, United Arab Emirates, 25 February 2016. EPA/ALI HAIDER

Tomas Berdych of the Czech Republic returns the ball to Nick Kyrgios of Australia during their quarter final match of the Dubai Duty Free Tennis ATP Championships in Dubai, United Arab Emirates, 25 February 2016. EPA/ALI HAIDER

Philipp Kohlschreiber of Germany returns the ball to Stanislas Wawrinka of Switzerland during their quarter final match of the Dubai Duty Free Tennis ATP Championships in Dubai, United Arab Emirates, 25 February 2016. EPA/ALI HAIDER

Stanislas Wawrinka of Switzerland returns the ball to Philipp Kohlschreiber of Germany during their quarter final match of the Dubai Duty Free Tennis ATP Championships in Dubai, United Arab Emirates, 25 February 2016. EPA/ALI HAIDER