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 to reach the WTA Quebec City quarter-finals.
Kristina Mladenovic during a US Open match in New York on August 26, 2014
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 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.