The 26-year-old Martinez Sanchez, ranked 54th in the world, powered to a 7-5, 6-4 win at the claycourt event to deprive the Dane of a what would have been a welcome present on her 19th birthday.
“You played better, congratulations, but I was hoping for a present for my birthday,” said Wozniacki, ranked ninth in the WTA standings and playing her sixth final of the year.
Martinez Sanchez responded: “Unfortunately I couldn’t give you a birthday present but I’ll invite you out for a nice dinner tonight.”
The Spaniard had been playing spoiler all week long, coming into the international tournament in Båstad unseeded and taking out number four seed Kaia Kanepi and number seven seed Carla Suarez Navarro on the way to the final.
She used her claycourt game to out-fox Wozniacki in many of their rallies, but had to rally from 1-4 down to win the 49-minute second set.