Fabio Fognini of Italy returns a ball to Dominic Thiem of Austria during their second round match at the BMW Open tennis tournament in Munich, Germany, 30 April 2015. EPA/MARC MUELLER

Guillermo Garcia-Lopez of Spain returns a ball to Kevin Anderson of South Africa during their second round match at the Millennium Estoril Open in in Estoril, Portugal, 30 April 2015. EPA/TIAGO PETINGA

Dominic Thiem of Austria returns a ball to Fabio Fognini of Italy during their second round match at the BMW Open tennis tournament in Munich, Germany, 30 April 2015. EPA/MARC MUELLER

Grigor Dimitrov of Bulgaria serves the ball to Andrey Golubev of Kazakhistan during their first round match of the TEB BNP Paribas Istanbul Open tennis tournament in Istanbul, Turkey, 30 April 2015. EPA/TOLGA BOZOGLU

Andy Murray of Great Britain reacts to a point against Mischa Zverev of Germany during their second round match for the ATP Tennis Tournament in Munich, Germany, 30 April 2015. EPA/MARC MUELLER