Quebec City - Kazakstan's Sesil Karatantcheva, seeking her first WTA title, rallied to defeat French third seed Kristina Mladenovic 5-7, 6-4, 7-5 on Wednesday to reach the WTA Quebec City quarter-finals.
Karatantcheva, ranked 195th, benefitted from 11 double faults by Mladenovic to advance. She will next face either Hungarian eighth seed Timea Babos or Croatian Mirjana Lucic-Baroni.
Booking a last-eight date were US fourth seed Shelby Rogers and Germany's Tatjana Maria.
Rogers outlasted compatriot Asia Muhammad 6-7 (5/7), 7-6 (7/2), 7-6 (7/5) while Maria ousted American Madison Brengle 4-6, 6-4, 6-0.
Czech Andrea Hlavackova opened by defeating Poland's Paula Kania 6-3, 6-0. She will face Croatian second seed Ajla Tomljanovic in a Thursday second-round matchup.
US top seed Venus Williams, a seven-time Grand Slam singles champion, faces Ukraine's Olga Savchuk in another second-round match on Thursday.
Williams, 34, is ranked 19th and comes off a third-round exit at the US Open. She seeks her 46th career WTA crown and second of the year after a triumph in Dubai.
Results on Wednesday from the third day of Quebec City WTA tournament (x denotes seed):
Tatjana Maria (GER) bt Madison Brengle (USA) 4-6, 6-4, 6-0
Shelby Rogers (USA x4) bt Asia Muhammad (USA) 6-7 (5/7), 7-6 (7/2), 7-6 (7/5)
Sesil Karatantcheva (KAZ) bt Kristina Mladenovic (FRA x3) 5-7, 6-4, 7-5
Julia Goerges (GER x5) bt Melanie Oudin (USA) 6-2, 6-2
Andrea Hlavackova (CZE) bt Paula Kania (POL) 6-3, 6-0