Dustin Brown of Germany hits a shot to Steve Johnson of the US in their second round Memphis Open tennis match at the Racquet Club of Memphis in Memphis, Tennessee, USA, 12 February 2015. EPA/TANNEN MAURY

Alexandr Dolgopolov of Ukraine hits a return shot to Bernard Tomic of Australia in their second round Memphis Open tennis match at the Racquet Club of Memphis in Memphis, Tennessee, USA, 12 February 2015. EPA/TANNEN MAURY

Kevin Anderson of South Africa serves to Sam Groth of Australia in their second round Memphis Open tennis match at the Racquet Club of Memphis in Memphis, Tennessee, USA, 12 February 2015. EPA/TANNEN MAURY

Bernard Tomic of Australia charges to attempt a return shot to Alexandr Dolgopolov of Ukraine in their second round Memphis Open tennis match at the Racquet Club of Memphis in Memphis, Tennessee, USA, 12 February 2015. EPA/TANNEN MAURY

Steve Johnson of the US charges to hit a return shot to Dustin Brown of Germany in their second round Memphis Open tennis match at the Racquet Club of Memphis in Memphis, Tennessee, USA, 12 February 2015. EPA/TANNEN MAURY

Donald Young of the US hits a return shot to Denis Kudla of the US in their second round Memphis Open tennis match at the Racquet Club of Memphis in Memphis, Tennessee, USA, 12 February 2015. EPA/TANNEN MAURY