This marks his first such feat since 2019 after ending a disrupted initial day of the 80th annual Rally Poland in the country's northeastern Mazuria region.
Mikkelsen was the fastest in Poland in 2016.
The Norwegian led from the start over the loose gravel roads in northern Poland and was 7.4 seconds clear before late stand-in Rovanpera and third placed Toyota team mate Elfyn Evans hit back.
Rovanpera was drafted in at the last moment to replace French driver Sébastien Ogier, a two-time Rally Poland winner and an eight-time world champion, who had to withdraw from the event after suffering a minor accident during a reconnaissance drive.
The three top crews were separated by just two seconds after stages three and seven were cancelled due to spectators standing in dangerous positions, leaving drivers and other fans frustrated.
"It is a shame we couldn’t do more stages, but all in all a positive day," said Mikkelsen.
Hyundai's championship contender Ott Tanak retired on stage two after a deer jumped into his car's path, causing an unavoidable collision and significant damage with the car travelling at around 190kph.
The Estonian and co-driver Martin Jarveoja were expected to return on Saturday after repairs.
The world's top drivers are battling for honours in the 80th annual Rally Poland.
In all, 42 crews from 23 countries are taking part, including some from as far afield as Bolivia, Argentina and Peru.
The rally opened on Thursday in the northeastern lakeside resort of Mikołajki and runs until Sunday.
(mo)
Source: Reuters