The reigning world champion delivered a dominant display to reel off the fastest times in all six of Friday's stages to open up a commanding 56.9s lead over Toyota team-mate Elfyn Evans.
Rovanpera's most impressive drive arrived in stage four where he was 11.1s faster than nearest rival Hyundai's Ott Tanak, who retired from the day two stages later. Tanak had managed to stay within 18.6s of the Toyota driver before crashing out on stage six.
Reflecting on his lead, Rovanpera admitted that he cannot afford to relax given the gruelling nature of the Safari Rally, and how quickly the event can turn on its head, especially if rain showers arrive.
"It has not been so easy, but it has been a good day for sure," said Rovanpera, making the second start of a partial WRC campaign this week.
"The plan was to use our starting place well and push when it is clear and still have a bit of margin to take care in the rough places in the afternoon, and still do good times, so I am happy.
"I wouldn't say it [the lead] is enough and not even close to being enough. If there are some big rain showers tomorrow or something comes, we have seen before the gaps can be huge.
"If you get any small issues then they [my rivals] can make big gaps so I'm not thinking about the time difference too much. For sure, it is good, but we need to work the same way tomorrow and then after tomorrow we can see where we are.
"When it rains here it rains a lot so you can have a lot of standing water and basically all the clay and stuff on the ground turns to really slippy mud and it is like going on ice. The grip is zero and you need to fight even on the straights to keep the car on the road."
Rovanpera's performance aside, Toyota enjoyed a strong Friday occupying the top three positions, with Evans second and Takamoto Katsuta third. Although, Hyundai's Thierry Neuville will begin Saturday's stages, 10.4s behind Evans.
"We have to be very happy with our cars being reliable and our drivers being patient and having a 1-2-3 at the end of the day is fantastic," said Toyota team principal Jari-Matti Latvala. "But Thierry is close so for sure he is pushing and will put pressure on us.
"Kalle has almost a one-minute lead so he has some flexibility but with Elfyn and Taka the gap back to Thierry is quite small so they can't really back off. The most important thing tomorrow is to be patient because if the rain comes it will be about survival."
