Ernest Gulbis of Latvia in action against Novak Djokovic of Serbia during their quarterfinal match of the Open ATP tennis tournament in Montreal, Canada, 14 August 2015. EPA/ANDRE PICHETTE

The game between John Isner of the US and Jeremy Chardy of France is delayed by rain during the Open ATP tennis tournament in Montreal, Canada, 14 August 2015. EPA/ANDRE PICHETTE

Novak Djokovic of Serbia in action against Ernest Gulbis of Latvia during their quarterfinal match at the Open ATP tennis tournament in Montreal, Canada, 14 August 2015. EPA/ANDRE PICHETTE

John Isner of the US returns a ball to Jeremy Chardy of France during their quarterfinal match of the Open ATP tennis tournament in Montreal, Canada, 14 August 2015. EPA/ANDRE PICHETTE

Jeremy Chardy of France returns the ball to John Isner of the US during their quarterfinal match of the Open ATP tennis tournament in Montreal, Canada, 14 August 2015. EPA/ANDRE PICHETTE