Top seed Caroline Garcia crashed out in the second round of the Ladies Championship Gstaad as Tereza Martincova earned her first top-20 win.
Martincova is ranked 120 places below world number 20 Garcia but claimed a 7-5 7-6 (7-1) triumph in Switzerland.
Garcia spurned five set points in the first set and, although she recovered from 5-2 down in the second, it was Martincova who dominated the tie-break to progress.
"It's amazing for me, really, because it was such a tough match," Martincova said. "She's a really good player. I played every single point and when we started, I was so nervous. But I really like her and her game; for me, I don't know what to say.
"We played before on hard courts, which is my favourite surface, but we played in the evening and I had some problems with my eyes. I wasn't as nervous this time, but come on, she's still top 20."
By contrast second seed Kiki Bertens made light work of qualifier Anna Zaja, winning 6-4 6-2, but Johanna Larsson needed three sets to see off Barbara Haas 1-6 7-5 6-1. Antonia Lottner beat Patty Schnyder 7-6 (7-0) 2-6 6-3.
There were also shocks at the Bucharest Open as Pauline Parmentier knocked out fifth seed Elise Mertens 3-6 6-4 6-4 after two hours, 22 minutes.
Qualifier Alexandra Dulgheru needed six minutes more to defeat ninth seed Ekaterina Alexandrova 6-4 4-6 6-2 while seventh seed Irina-Camelia Begu saw off Romanian compatriot Jaqueline Christian 6-4 6-0 and Tatjana Maria's opponent Nadia Podoroska retired at 4-1 down in the first set.