Tommy Paul of the US follows through on a return backhand shot to Benjamin Becker of Germany in their first round match of the Memphis Open tennis championship at the Racquet Club of Memphis in Memphis, Tennessee, USA, 09 February 2016. EPA/TANNEN MAURY

Marin Cilic of Croatia returns the ball to Denis Istomin of Uzbekistan during their first round match of the ABN AMRO World Tennis Tournament in Rotterdam, Netherlands, 08 February 2016. EPA/KOEN SUYK

Taylor Fritz of the US hits a return shot to Michael Mmoh of the US in their round match of the Memphis Open tennis championship at the Racquet Club of Memphis in Memphis, Tennessee, USA, 09 February 2016. EPA/TANNEN MAURY

France’s Gilles Simon in action against Robin Haase of the Netherlands during their first round match of the ABN AMRO World Tennis Tournament in Rotterdam, Netherlands, 10 February 2016. EPA/KOEN SUYK

Austin Krajicek of the US (back) watches as doubles partner Nicholas Monroe of the US (front) hits a return shot to Mike and Bob Bryan in their first round doubles match of the Memphis Open tennis championship at the Racquet Club of Memphis in Memphis, Tennessee, USA, 09 February 2016. EPA/TANNEN MAURY