British number Heather Watson failed to book a rematch with Serena Williams after falling at the second hurdle of the Rogers Cup.
The 23-year-old, who came so close to eliminating eventual winner Williams from Wimbledon last month, made light work of Irina Falconi in the opening round but could not keep Germany's 16th seed Andrea Petkovic under wraps in Toronto on Wednesday.
Petkovic took full advantage of Watson's faltering first serve to win 6-4 6-3 and it is she who will now face top seed and world number one Williams.
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Second seed Simona Halep is safely through after beating Jelena Jankovic 6-3 6-4 but there were upsets for both fourth seed Caroline Wozniacki and seventh seed Lucie Safarova, who lost to Belinda Bencic and Daria Gavrilova respectively.
Swiss teenager Bencic - a 7-5 7-5 victor over Wozniacki on Wednesday - will tackle former Wimbledon finalist Sabine Lisicki following the German's 7-6 (7/3) 6-4 conquest of Barbora Strycova while Gavrilova is paired with Roberta Vinci, the Italian who ousted Mirjana Lucic-Baroni 6-3 6-3.
The draw has pitted Polona Hercog against Ana Ivanovic. The former player trumped 11th seed Ekaterina Makarova 6-2 6-7 (2/7) 7-5 and Ivanovic dispatched Olga Govortsova 6-4 7-6 (7/4).
Also winning through were Lesia Tsurenko, Sara Errani, Carina Witthoeft, Alize Cornet and 13th seed Angelique Kerber.
Third seed Petra Kvitova is out after suffering a 6-2 6-3 loss to Victoria Azarenka, but sixth seed Agnieszka Radwanska had no such trouble in dispatching Julia Goerges 7-5 6-3.