Karolina Pliskova fired 16 aces to upset eighth-seeded Czech compatriot Lucie Safarova 7-6 (4) 4-6, 7-5 at the WTA Porsche Grand Prix on Wednesday.
Safarova had 12 aces but also produced nine double-faults in the first-round match.
Sixth-seeded Roberta Vinci of Italy advanced in the indoor clay-court event by outlasting Ekaterina Makarova of Russia 7-6 (3), 4-6, 6-4.
Andrea Petkovic of Germany beat Kristina Mladenovic of France 6-2, 6-4 and wild card Julia Goerges of Germany breezed past Alize Cornet of France 6-4, 6-0. Monica Niculescu of Romania defeated another Frenchwoman, Caroline Garcia, 6-2, 6-2.