Margarita Gasparyan came from behind to dump seventh seed Viktoria Kuzmova out of the Rosmalen Grass Court Championships.
The Russian recorded a second win over a player in the WTA Tour's top 50 this season, taking two hours and 23 minutes to triumph 2-6 7-6 (7-5) 6-4 in the first round to earn a first main-draw win on grass.
Gasparyan said: "It was such a tough match, I'm happy I came through! I love to play on grass."
Veronika Kudermetova, who defeated Caroline Wozniacki at the French Open, kept her cool when a long rain delay in the Netherlands stopped play as she was just one game away from sealing victory over Ons Jabeur.
She lost the first two games after the players made their return to court, but then secured a 6-3 6-4 win.
Elena Rybakina cruised to a 6-1 6-2 victory over Varvara Lepchenko, while Arantxa Rus edged an all-Dutch encounter against Bibiane Schoofs 7-5 6-4.
There were also wins for Paula Badosa Gibert and Greet Minnen, with top seeds Kiki Bertens and Aryna Sabalenka due to kick off their campaigns on Tuesday.
Rain meant no Monday play was possible at the Nottingham Open, where Caroline Garcia is seeded number one.