The Finn had started the day only three seconds clear of Hyundai's Thierry Neuville but reeled off nine stage wins in a row to go into Sunday's four remaining stages as the clear favourite.
"I have really enjoyed the afternoon," he said.
"It has been really nice. The car is working well and these are my favourite stages of the entire calendar, so why wouldn't I be enjoying them at full speed?"
Rovanpera became the youngest-ever winner of a world championship round with his triumph on Estonia's fast gravel roads two years ago and repeated the win in 2022.
Hyundai's Esapekka Lappi was running in third place, 10.5 seconds adrift of Belgian Neuville with Toyota's Elfyn Evans in fourth.
Sunday features two identical loops of two stages before the finish in Tartu.
