Qiang Wang of China returns the ball to Sloane Stephens of the USA during their first round match at the Australian Open Grand Slam tennis tournament in Melbourne, Australia, 18 January 2016. The Australian Open tennis tournament runs from 18 to 31 January 2016. EPA/MADE NAGI

Maria Sakkari of Greece hits a return against Wang Yafan of China during their first round match at the Australian Open Grand Slam tennis tournament in Melbourne, Australia, 18 January 2016. The Australian Open tennis tournament runs from 18 to 31 January 2016. EPA/MAST IRHAM

Novak Djokovic of Serbia returns the ball to Hyeon Chung of South Korea during the first round match of the Australian Open Grand Slam tennis tournament in Melbourne, Australia, 18 January 2016. The Australian Open tennis tournament runs from 18 to 31 January 2016. EPA/FILIP SINGER

A tennis fan covers himself with a towel during the first day of the of the Australian Open Grand Slam tennis tournament at Melbourne Park, in Melbourne, Australia, 18 January 2016. The Australian Open tennis tournament runs from 18 January until 31 Januray 2016 EPA/FILIP SINGER

Daria Gavrilova of Australia celebrates after winning against Lucie Hradecka of the Czech Republic during their first round match on day one of the Australian Open tennis tournament in Melbourne, Australia, 18 January 2016. The Australian Open tennis tournament runs from 18 to 31 January 2016. EPA/TRACEY

Kei Nishikori of Japan serves the ball to Germany’s Philipp Kohlschreiber during their first round match at the Australian Open Grand Slam tennis tournament in Melbourne, Australia, 18 January 2016. The Australian Open tennis tournament runs from 18 to 31 January 2016. EPA/MADE NAGI