Andrea Petkovic of Germany hits a return against Eugenie Bouchard of Canada during their first round women's singles match at the China Open tennis tournament in Beijing on October 5, 2015.

Andrea Petkovic of Germany hits a return against Eugenie Bouchard of Canada during their first round women's singles match at the China Open tennis tournament in Beijing on October

Serena Williams of U.S. holds her winning trophy and waves to her fans after the final of the China Open tennis tournament at the National Tennis Stadium in Beijing, China, Sunday, Oct. 6, 2013. Williams defeated Jelena Jankovic of Serbia 6-2, 6-2. (AP Photo)

Serena Williams of U.S. holds her winning trophy and waves to her fans after the final of the China Open tennis tournament at the National Tennis Stadium in Beijing, China, Sunday, Oct. 6, 2013. Williams defeated Jelena Jankovic of Serbia 6-2, 6-2. (AP Photo)

Agnieszka Radwanska of Poland hits a return against Johanna Konta of Britain during the women's singles final of the China Open tennis tournament in Beijing on October 9, 2016. / AFP / NICOLAS. Radwanska won the title 6-4, 6-2.

Agnieszka Radwanska of Poland hits a return against Johanna Konta of Britain during the women's singles final of the China Open tennis tournament in Beijing on October 9, 2016. / AFP / NICOLAS. Radwanska won the title 6-4, 6-2.

World No1 Novak Djokovic serving during his match against Lukas Rosol of the Czech Republic at the China Open tennis tournament in Beijing Petar Kujundzic

World No1 Novak Djokovic serving during his match against Lukas Rosol of the Czech Republic at the China Open tennis tournament in Beijing Petar Kujundzic

Spain's Rafael Nadal serves during his men's singles semi-final match against Tomas Berdych of the Czech Republic at the China Open tennis.

Spain's Rafael Nadal serves during his men's singles semi-final match against Tomas Berdych of the Czech Republic at the China Open tennis.

Richard Gasquet of France returns a shot to Novak Djokovic of Serbia during the semifinal match of the China Open tennis tournament at the National Tennis Stadium in Beijing, China Saturday, Oct. 5, 2013. (AP)

Richard Gasquet of France returns a shot to Novak Djokovic of Serbia during the semifinal match of the China Open tennis tournament at the National Tennis Stadium in Beijing, China Saturday, Oct. 5, 2013. (AP)

Garbine Muguruza Photos Photos - Garbine  Muguruza of Spain returns a shot against Ekaterina Makarova of the Russia during day two of the China Open at the China National Tennis Center on September 28, 2014 in Beijing, China. - 2014 China Open - Day 2

Garbine Muguruza Photos Photos: 2014 China Open - Day 2

Garbine Muguruza Photos Photos - Garbine Muguruza of Spain returns a shot against Ekaterina Makarova of the Russia during day two of the China Open at the China National Tennis Center on September 28, 2014 in Beijing, China. - 2014 China Open - Day 2

Eugenie Bouchard of Canada receives medical attention during her first round match against Andrea Petkovic of Germany in the China Open tennis tournament at the National Tennis Stadium in Beijing, Monday.

Eugenie Bouchard retires from opening match at China Open with dizziness

Eugenie Bouchard of Canada receives medical attention during her first round match against Andrea Petkovic of Germany in the China Open tennis tournament at the National Tennis Stadium in Beijing, Monday.

Andrea Petkovic of Germany serves during her women's singles match against Simona Halep of Romania at the China Open tennis tournament in Beijing October 2, 2014. (REUTERS/Petar Kujundzic)

Photos of the day - October 2, 2014

Andrea Petkovic of Germany serves during her women's singles match against Simona Halep of Romania at the China Open tennis tournament in Beijing October 2, 2014. (REUTERS/Petar Kujundzic)

Francesca Schiavone of Italy returns a volley from between her legs during her women's singles match against Samantha Stosur of Australia at the China Open tennis tournament in Beijing September 28, 2014. REUTERS-Petar Kujundzic

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Francesca Schiavone of Italy returns a volley from between her legs during her women's singles match against Samantha Stosur of Australia at the China Open tennis tournament in Beijing September 28, 2014. REUTERS-Petar Kujundzic

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