The Welshman, who won seven of eight stages on Saturday, romped to victory over Hyundai's Thierry Neuville by 39.1 seconds after also taking maximum bonus points from the final Power stage.
Rovanpera, who rolled out of his home event on Friday while leading, had his lead slashed from 55 points to 25 with four rallies remaining.
"It's been a pretty good weekend," said Evans of his second victory on Finland's fast gravel roads and seventh win of his WRC career.
"Of course we're sorry for the loss of Kalle at the start of the rally but after that it's been really fantastic to drive this car."
Toyota's Takamoto Katsuta was third, 57.6 seconds behind Neuville, for the Japanese driver's first podium in Europe.
Toyota increased its lead over Hyundai in the manufacturers' standings to 67 points.
The next round in Greece, the Acropolis Rally based in Lamia, is from September 7th-10th.
