The Polish tennis star Agnieszka Radwanska's hope of claiming world's top ranking ahead of the U.S. Open remains alive after she survived a testing first match in the Montreal Cup.
The Pole will replace Victoria Azarenka as world number one if she wins the event and the reigning Australian Open Champion Azarenka fails to reach the quarter-finals.
Radwanska, who was stretched all the way by German Mona Barthel on a day of upsets, came from a break down in the final set to win 4-6 6-3 7-6 (5).
The tournament second seed will play Chanelle Scheepers in the third-round.
Azarenka will be forced to wait until Saturday at the earliest to finish her match against Tamira Paszek after it was postponed due to rain.
The former world number one Ana Ivanovic failed to win a game when thrashed in just 44 minutes by Italian Roberta Vinci.
American Varvara Lepchenko upset 12th seed Dominika Cibulkova 6-4 6-4 and will next play either Caroline Wozniacki or Kiki Bertens.
The 10th seed, China's Li Na, beat Canadian Eugenie Bouchard 6-4 6-4 just while 15th seeded Sabine Lisicki of Germany lost 3-6 6-3 6-4 to Spaniard Carla Suarez Navarro.