The Danish second seed Caroline Wozniacki advanced to the third round of the $NZ 2.8 million WTA Montreal Cup, defeating Swiss Patty Schnyder 7-5 7-5.
Wozniacki passed Jankovic to become world Number two earlier this week and next faces Italy's Flavia Pennetta, who eliminated Russian Alisa Kleybanova 6-3 6-3.
Italian sixth seed Francesca Schiavone outlasted Russian Ekaterina Makarova 6-4 6-7 (5-7) 6-2 to book a third-round date against Russian Dinara Safina, who ousted compatriot Nadia Petrova 7-5 4-6 6-4.
Also advancing was Polish seventh seed Agnieszka Radwanska, who ousted American Vania King 6-love 6-3.
Japan's Kimiko Date Krumm withdrew due to a left quadriceps strain, handing France's Marion Bartoli a walkover into a match against Czech qualifier Iveta Benesova, who ousted Jankovic earlier in the week.
Victoria Azarenka of Belarus beat Russian Maria Kirilenko 6-4 6-1 to book a third-round match with China's Li Na, the ninth seed who took a bye after Williams pulled out and is now the highest seed in her quarter of the draw.