Denis Istomin of Uzbekistan returns the ball to Maxime Teixeira of France during their first round match at the Swiss Open tennis tournament in Gstaad, Switzerland, 27 July 2015. EPA/PETER SCHNEIDER

Nicolas Almagro of Spain in action during his first round match against Albert Ramos-Vinolas of Spain at the ATP tennis tournament in Hamburg, Germany, 27 July 2015. EPA/Bodo Marks

Maxime Teixeira of France returns the ball to Denis Istomin of Uzbekistan during their first round match at the Swiss Open tennis tournament in Gstaad, Switzerland, 27 July 2015. EPA/PETER SCHNEIDER

Andrey Rublev of Russia serves the ball to Horacio Zeballos of Argentina during their first round match at the Swiss Open tennis tournament in Gstaad, Switzerland, 27 July 2015. EPA/PETER SCHNEIDER

Spanish tennis player Rafael Nadal in action during a training session prior to the ATP tennis tournament in Hamburg, Germany, 27 July 2015. EPA/BODO MARKS

Taro Daniel of Japan in action against Jerzy Janowicz of Poland during their first round match of the ATP tennis tournament in Hamburg, Germany, 27 July 2015. EPA/BODO MARKS