World number 70 Donna Vekic stunned top seed Johanna Konta by coming from behind to win the final of the grass-court Aegon Open in Nottingham.
Britain's Konta, the world number eight, looked on course for a first tournament win on home soil as she made a superb start but Croatian Vekic hit back to win 2-6 7-6 (7/3) 7-5.
It was her second career singles title and a first on grass, providing a big confidence boost ahead of Wimbledon next month.
"It's pretty amazing," 20-year-old Vekic said on Eurosport. "I'm really happy. Jo played amazing, she's having an amazing year, but I was just trying to focus on myself and serve as good as I can and be aggressive."
Konta seemed determined to claim her first grass-court title as she broke in the first game of the match and then powered through the opening set.
Vekic's recovery started as she broke to lead 3-1 in the second set. Konta immediately broke back but there were signs of frustration from the home favourite as she disputed a line call.
Konta lost the set on a tie-break and there was further anguish early in the decider as she contested another decision.
Again Konta fell 3-1 behind but after recovering to draw back level and then lead, it seemed she had overcome a mid-match wobble.
But after serving to stay in the match, Vekic claimed a crucial break and then served out for victory.
"All credit to Donna, she was continuously able to raise her level all throughout that match," Konta said. "I was not able to stay with her."
In s-Hertogenbosch, the unseeded Estonian Anett Kontaveit overpowered Natalia Vikhlyantseva 6-2 6-3 to win the Ricoh Open.
Kontaveit built momentum after saving two break points in the third game of the match and eased through the first set.
She fell 3-1 down in the second but turned the tide by winning 10 successive points and did not look back.