Rain last week in Montreal forced the postponement of the Rogers Cup finale until Monday night, when the Czech Republic's Kvitova prevailed over Li Na of China for her first title of the year.
But the short turnaround didn't seem to affect the fourth-seeded Kvitova, who came from behind to best German Mona Barthel 3-6, 6-2, 7-5 on the hard courts at the Lindner Family Tennis Center.
She'll next face China's Peng Shuai, who bested Italian Roberta Vinci 6-3, 6-4 Wednesday.
Top-seeded Agnieszka Radwanska of Poland also advanced, dismissing Sweden's Sofia Arvidsson 6-4, 6-3. Her next opponent will be American Sloane Stephens, who routed Italian and fellow wild card Camila Giorgi 6-2, 6-1.
American favorite Venus Williams also moved on with a 2-6, 6-2, 6-2 comeback win over South African Chanelle Scheepers.
Other winners Wednesday included seventh-seeded Sara Errani, Czech qualifier Andrea Hlavackova, Russians Anastasia Pavlyuchenkova and Ekaterina Makarova and Agnieszka Radwanska's younger sister Urszula.