Magdalena Rybarikova claimed the scalp of Karolina Pliskova in the first round of the Birmingham Classic and Anett Kontaveit was among three seeds to crash out of the Mallorca Open on day one.
Rybarikova beat Pliskova at Wimbledon last year and history repeated itself when the unseeded Slovakian saw off the world number seven 6-2 6-3 on Monday.
Pliskova was thrashed by Maria Sharapova in the third round of the French Open and started her grass-court season in disappointing fashion at Edgbaston Priory Club.
The 19-ranked Rybarikova served eight aces and won 81 per cent of points on her first serve in a commanding victory, which was sealed with a fourth break.
Rybarikova's second-round opponent will be Kristina Mladenovic, who recovered from a poor start to beat Katerina Siniakova 1-6 6-2 6-4.
Naomi Osaka beat Katie Boulter in her homeland, while Daria Gavrilova got the better of Dominika Cibulkova.
Kontaveit fell at the first hurdle in Mallorca, where Tatjana Maria came from a set down to defeat the fourth seed 3-6 6-4 6-3.
Fourth seed Carla Suarez Navarro went down 6-4 7-6 (7-4) to fellow Spaniard Lara Arruabarrena, while Alison Van Uytvanck toppled eighth seed Aryna Sabalenka 3-6 6-4 6-2.
Carina Witthoeft and Samantha Stosur were the other first-round winners.