Top-seeded Eugenie Bouchard overcame a slow start to beat Patricia Mayr-Achleitner of Austria 6-4, 6-1 in the opening round of the Generali Ladies on Wednesday.
Bouchard dropped her opening service game and the Wimbledon finalist failed to shrug off her 100th-ranked opponent until 4-4. The sixth-ranked Canadian then won six straight games and smoothly closed out the win.
Bouchard and No. 7 Karolina Pliskova of the Czech Republic are the only seeded players left in the tournament after the first round.
No. 2 Ana Ivanovic pulled out injured while No. 3 Dominika Cibulkova and No. 5 Sabine Lisicki both slipped to three-set defeats on Wednesday.
Two-time former champion Ivanovic withdrew with a hip complaint one day after receiving medical treatment during her first-round win over Pauline Parmentier of France.
"This injury has been plaguing me the whole summer, and it got worse during the recent tournaments in Asia," Ivanovic said in a statement on the tournament website. "I am sorry but I can't play on."
The eighth-ranked Ivanovic, who won the indoor hard-court event in Austria in 2008 and 2010 and reached the final last year, has qualified for the WTA Finals in Singapore.
Her withdrawal advanced Madison Brengle of the United States to her first career quarterfinal.
Anna-Lena Friedsam of Germany rallied to defeat Cibulkova 2-6, 6-3, 6-4. The 94th-ranked Friedsam missed two match points while serving at 5-2 but converted the fourth chance in her next service game.
Karin Knapp of Italy beat Lisicki 7-5, 2-6, 7-6 (1) after failing to serve out the match at 5-3 in the final set.
In second-round play, Stefanie Voegele of Switzerland advanced to her fourth quarterfinal of the season by rallying to defeat Anna Schmiedlova of Slovakia 2-6, 6-1, 6-4.
Camila Giorgi of Italy saved 10 of 11 break points while beating Ons Jabeur of Tunisia 6-3, 6-2 to set up a quarterfinal against Marina Erakovic of New Zealand, who routed Klara Koukalova of Czech Republic 6-0, 6-2.
Erakovic had six aces to earn her first quarterfinal since reaching the semifinals in Washington in July.