Title contender Evans had one of the best stage loops of his WRC career, winning all four gravel tests to beat the Hyundais of Ott Tanak and overnight leader Craig Breen.
As a result, Evans finished the morning 5.6 seconds ahead of Breen while Tanak is 9.7 seconds behind.
However, the big story of the morning was the disappearance of Rovanpera, who crashed on the last leg of the loop.
The Finn had struggled for pace in the previous three stages, moving away from the battle for the lead in fourth place when drama struck. Rovanpera lost the back of his Yaris in stage 10 before sinking into a pile of gravel, placed in front of a telegraph pole, causing damage to the front of the car.
Wildcard Toyota rider Esapekka Lappi finished the morning fourth overall, ahead of Thierry Neuville, while championship leader Sébastien Ogier, struggling for confidence, was more than a minute from the pace.
The fierce header battle resumed in earnest in the opening leg of the day which was won by Evans, who said his feeling was “even better” than Friday.
The Welshman was the most confident of his rivals on slippery gravel, posting a time 0.2 seconds faster than rally leader Breen, who continued to impress in his last outing for Hyundai this season.
Breen felt, however, that he had lost time in the stage by hesitation.
“I left so much time there five or eight seconds easily with hesitation,” Breen said. “I just have to keep the balls on the scoreboard and keep going. It was a great race that I really enjoyed. The race is on.”
Tanak was part of a group of pilots struggling with confidence to push hard as he lost 1.4 seconds to Evans.
Rovanpera did not fare as well dropping 4.6 seconds, but managed to beat compatriot Lappi to move up to fourth place overall, albeit behind on Friday night.
“It was a clean race, but I’m not completely happy with the car and myself,” said Rovanpera. “It’s harder than it should be – I can’t be as specific as I want to be, but there’s not much we can do now.”
Neuville responded with a poor end on Friday to finish the fourth fastest stage, while Ogier continued to fight for outright speed.
The rally changed face in the next stage as Evans moved up from third to rally leader after his best driving of the event so far.
Evans blitzed Stage 8 by winning the test by 4.2 seconds ahead of Tanak, but crucially took Breen 6.2 seconds to open an overall lead of 0.9 seconds.
“I’ll go a little faster,” Breen said. “Compared to Ott, it’s not a bad stage, but Elfyn did a real shield in there. I had a bit of trouble with the grip, but it’s an incredible time.”
Neuville’s resurgence continued to set a faster time than Rovanpera as the latter continued to retreat even further from the lead.
“I knew this stage was going to be difficult and there is nothing more I can do,” said Rovanpera. “I’m just trying to survive on the road – I slide so much and just don’t have the grip to do anything else.”
However, the worst was to befall Rovanpera’s teammate Katsuta as he retreated after chopping a tree down on the stage, damaging the Yaris’ right-back who pulled into the road and s ‘is found stuck in the undergrowth.
Evans continued his streak of stage victories in the penultimate round of the morning to further extend his overall advantage over Breen.
This time around, the Toyota driver’s closest rival was his teammate Rovanpera, who found an improved pace, to finish the stage in just 1.6 seconds.
Breen lost 3.1 seconds against the new leader while Tanak lost six more tenths.
Evans completed his dominant display by winning the final test 1.6sec from Breen, while Tanak was 3.7s away.
Earlier in the test, Rovanpera crashed, allowing Lappi, the only Finn remaining, to climb to fourth place overall.
Rally Finland continues on Saturday afternoon with a second run through the morning stages followed by a repeat of the opening stage on Friday under the lights.