Rovanpera flipped his Toyota over on its roof after losing control on a rain-hit forest mud track during the eighth stage.
Both Rovanpera and his co-driver Jonne Halttunen were unharmed but unable to continue in his heavily damaged car.
Rovanpera's accident came hours after Ott Tanak's (35) hopes went up in smoke when the 2019 world champion was forced to retire his stricken M-Sport Ford.
The Estonian led the ninth leg of the rally world championship after Thursday's super stage.
But mechanical failure in the third stage triggered his premature exit from an event he has won three times.
"Due to impact damage on SS3, sadly we have been left with no choice but to retire Ott's car from Rally Finland," his team confirmed.
This setback follows the five-minute penalty he incurred for an engine change before his home rally in Estonia last time out.
"Of course we are disappointed, after Estonia this isn't how we wanted this week to go," Tanak, the 2019 champion, told wrc.com.
"It's a shame we can't continue but the car is too damaged for us to carry on.
"Now it's time to have a break after a busy few months, then we will focus fully on Greece in September."
Tanak's turmoil left series leader and home favourite Rovanpera to take command.
The Toyota driver reeled off five stage wins in a row to lead his teammate Elfyn Evans (34) by almost six seconds.
But his dramatic loss of control left Evans in the overall lead with two of Friday's stages remaining.
