The Welsh driver claimed seven of the day's eight stages with fellow Toyota driver Takamoto Katsuta of Japan winning the other on the course's mud-filled tracks.
"It's good to be in this position but there are still four special stages tomorrow," said Evans who has a commanding 32.1sec lead over Belgium's Thierry Neuville of Hyundai.
Neuville admitted that his chances of overhauling Evans on Sunday were slim.
"I'm not really pushing. Everything is going well but I can't do more. We're too far now and we have to keep going in case something happens but we don't have the means to fight for the win," he said.
The battle for third place is closer with Katsuta having a 6.4-sec lead over Finland's Teemu Suninen of Hyundai.
Rovanpera, the championship leader with a 55-point lead over Evans, was the overwhelming favourite to win in Finland.
However, a mistake while leading the race on Friday saw him roll his Toyota on its roof.
He was unable to return to the action on Saturday where he had been hoping to score points in the power stage which brings additional championship points.
Rovanpera will still retain his overall lead in the standings with a maximum 30 points only on offer for Evans on Sunday.
