David Ferrer of Spain hits a return to Damir Dzumhur of Bosnia and Herzegovina during the second day of the 2014 US Open Tennis Championship at the USTA National Tennis Center in Flushing, Meadows, New York, USA, 26 August 2014. The US Open runs through 08 September, a 15-day schedule. EPA/JUSTIN LANE

Lauren Davis of the US hits a return to Samantha Stosur of Australia during the second day of the 2014 US Open Tennis Championship at the USTA National Tennis Center in Flushing, Meadows, New York, USA, 26 August 2014. The US Open runs through 08 September, a 15-day schedule. EPA/JUSTIN LANE

Misaki Doi of Japan hits a return to Victoria Azarenka of Belarus during the second day of the 2014 US Open Tennis Championship at the USTA National Tennis Center in Flushing, Meadows, New York, USA, 26 August 2014. The US Open runs through 08 September, a 15-day schedule. EPA/JUSTIN LANE

Marcos Giron of the US hits a return between his legs to John Isner of the US during the second day of the 2014 US Open Tennis Championship at the USTA National Tennis Center in Flushing, Meadows, New York, USA, 26 August 2014. The US Open runs through 08 September, a 15-day schedule. EPA/JOHN G. MABANGLO

Petra Kvitova of the Czech Republic hits a return to Kristina Mladenovic of France during the second day of the 2014 US Open Tennis Championship at the USTA National Tennis Center in Flushing, Meadows, New York, USA, 26 August 2014. The US Open runs through 08 September, a 15-day schedule. EPA/JOHN G. MABANGLO

John Isner of the US serves to Marcos Giron of the US during the second day of the 2014 US Open Tennis Championship at the USTA National Tennis Center in Flushing, Meadows, New York, USA, 26 August 2014. The US Open runs through 08 September, a 15-day schedule. EPA/JOHN G. MABANGLO