Venus Williams, Garbine Muguruza advance into Rogers Cup last 16

Katerina Siniakova of the Czech Republic hits a forehand during her loss to Venus Williams of the United States in the Rogers Cup women's tennis tournament in Toronto. | AP

Venus Williams of the United States hits a backhand on her way to defeating Katerina Siniakova of the Czech Republic during the Rogers Cup women's tennis tournament in Toronto. | AP

Katerina Siniakova of the Czech Republic hits a backhand during her loss to Venus Williams of the United States in the Rogers Cup women's tennis tournament in Toronto. | AP

Garbine Muguruza of Spain hits a backhand return against Kirsten Flipkens of Belgium during the Rogers Cup women's tennis tournament in Toronto. | AP

Kirsten Flipkens, of Belgium, eyes a return against Garbine Muguruza, of Spain, durng the Rogers Cup women's tennis tournament in Toronto. | AP

Garbine Muguruza of Spain eyes a shot against Kirsten Flipkens of Belgium during the Rogers Cup women's tennis tournament in Toronto. | AP

Karolina Pliskova, of the Czech Republic, hits a return to Anastasia Pavlyuchenkova, of Russia, during the Rogers Cup women's tennis tournament in Toronto. | AP

Anastasia Pavlyuchenkova, of Russia, hits a return to Karolina Pliskova, of the Czech Republic, during the Rogers Cup women's tennis tournament in Toronto. | AP

Karolina Pliskova of the Czech Republic hits a backhand shot against Anastasia Pavlyuchenkova of Russia during the Rogers Cup women's tennis tournament in Toronto. | AP