The 22-year-old Finn split the stage wins with his team-mate Elfyn Evans, heading the Welshman home by 11.6 seconds after a sodden day’s sport on the stages close to Tampere.
Rovanperä said he hoped the rain would continue into this week’s Jyväskylä-based event.
“I hope it will be a bit wet,” said the WRC points leader. “It would be good to use this set-up. We had a really good preparation – we were able to confirm everything we tried in the pre-event test at this rally in Tampere. I’ve never done this one before, so it was good to come here and take the win – it was really nice to see the fans!
“The conditions were quite extreme with the rain and the mud, but the car was working really well. This week will be a bit more of a challenge, but we’re ready for it.”