The Toyota driver started the day with a 10.8s advantage but a stunning drive to sweep the trio of stages allowed the Finn to open up a 52.4s lead over Hyundai’s Dani Sordo.
Sordo's team-mate Esapekka Lappi has moved to third but 57.0s adrift, ahead of the third Hyundai of Thierry Neuville (+57.9s) and M-Sport’s Ott Tanak (+1m34.1s) after Pierre-Louis Loubet crashed his Ford out of fifth on stage 10.
Rovanpera produced the drive of the rally to date on stage nine, the 26.61km Vieira do Minho, after delivering a mesmerising time that was 12.8s faster than Lappi's next best.
Making the most of the starting last of the Rally1 runners, Rovanpera more than doubled his overall rally lead on his way to fifth stage win of the rally.
When asked to explain his speed, he replied: “I just woke up today and thought we should drive a bit of rally, so that is what we tried to do.”
Lappi was unhappy with his performance, but it was enough to climb from fifth to third overall. His effort was 0.5s quicker than Sordo as he began to chip away at the gap between his more experienced team-mate sitting second overall.
Neuville moved his Hyundai up to fourth after M-Sport’s Loubet suffered damage to his rear wing and dropped 6.6s to the Belgian.
The battle at the front changed complexion again on stage 10 after Rovanpera won the 37.24km pass through Amarante, the longest of the rally. The Finn was 3.3s faster than Tanak, who was continuing his recovery from a puncture on Friday’s stage four but struggling with his Puma.
“We could improve the balance a bit from the previous stage, but I am still having quite a massive struggle with the suspension," he said.
"I'm still riding this wild horse. It is like I've never driven a rally car before, it's so challenging.”
Rovanpera’s lead ballooned to 45.8s courtesy of a struggling Sordo, who was battling with his soft tyres. Sordo’s time loss, combined with Lappi’s improved pace, brought the latter back into the fight for second overall.
The leaderboard did however undergo a change when Loubet crashed out of the rally less than a kilometre from the stage end. The Frenchman clipped a bank with his left front, which appeared to break the steering and send his Puma across the road into another bank.
The stage continued with the car partially blocking the road, which required drivers to slow down to navigate around the stricken car.
“It is a very small mistake he has made, but unfortunately it has put him out for the day,” said M-Sport team principal Richard Millener.
“It is really frustrating for him, but there is positives to take. I know for a fact that will be difficult for him to concentrate on right at this moment. It is really disappointing for him.”
Rovanpera completed his perfect morning by winning stage 11 by 5.7s from Neuville, with Sordo a further 0.9s slower. Lappi meanwhile dropped time to Neuville, which reduced the gap between the pair to 0.9s.
The stage wasn’t without drama as Takamoto Katsuta, who rejoined the rally after Friday’s alternator failure, spun during the test. The Japanese recovered to reach the stage finish.
Despite a spin on stage nine, Oliver Solberg led Toksport team-mate Gus Greensmith by 37.0s in WRC2. The crews will tackle four more stages this afternoon following a midday service.
