Beatriz Recari struck a six-under-par opening round to establish a one-stroke lead in the Finnair Masters in Helsinki.
The 22-year-old Spaniard claimed seven birdies, with the only blemish coming in the par-four 18th in her round of 65.
Iben Tinning of Denmark, meanwhile, birdied the same hole to put herself clear in second.
Recari, who also led after the first round last year, told www.ladieseuropeantour.info: "Overall I think I did a great job mental wise on every single shot.
"I'm not going to punish myself for a bogey on the last because six-under is quite good and I have a good feeling for tomorrow."
Becky Brewerton of Wales claimed a share of third place with a four-under round of 67, alongside Sweden's Johanna Westerberg, South African Lee-Anne Pace Je-Yoon Yang, the 17-year-old South Korean amateur.