The two-time world champion Finn, who is yet to win his home round of the FIA WRC, heads GR Yaris Rally1 Hybrid team-mate Elfyn Evans after winning four of today’s nine stages. Sébastien Ogier rounds out the top three, just 0.6s further back.

In stark contrast, rival team Hyundai endured a tough day, with two of its i20 N Rally1 Hybrid cars crashing out. Title hopeful Ott Tänak was forced out by a roll on SS3, which resulted in co-driver Martin Järveoja being taken to hospital for medical checks where he will remain overnight for monitoring. Meanwhile, Esapekka Lappi retired from fourth after hitting a tree, which tore the rear suspension from his car. Lappi is expected to restart on Saturday.

Rovanperä overcame excessive oversteer in the early stages to hold a slender lead of 0.2s over Evans at the day’s midpoint, but he raised the bar on the repeated afternoon loop to widen that gap as the rain-hit tracks became rutted and even more challenging.

The omens look good for the 24-year-old as, for the past two years, Friday night's leader has gone on to win.

“It has been a tricky day, especially with the weather,” Rovanperä said. “Really changeable and difficult conditions, so I am quite happy to have had a clean day.

“Tomorrow will be difficult for sure - I think there has been a lot of rain on those stages also but we will see how it is in the morning. All the guys are pushing hard and the gaps are really small, so it’s going to be a big fight.”

Championship leader Thierry Neuville is Hyundai’s main hope for a strong result. Climbing the standings after the retirements of his team-mates plus Takamoto Katsuta’s crash on SS5, he holds fourth overnight but was hindered by his car’s set-up and an overshoot in the morning. The Belgian trails Ogier by 16.9s at close of play and, as it stands, is set for his points buffer over title rival Evans shrink.

The lack of a pre-rally test meant Adrien Fourmaux had to adjust the set-up of his M-Sport Ford Puma Rally1 Hybrid on road sections between stages. Holding fifth with a 42.5s buffer over Sami Pajari, the Frenchman felt he had made good progress with the car by the end of the leg.

Pajari’s day was one of two halves. Two spins left the GR Yaris Rally1 Hybrid rookie end the first stage with a damaged rear wing, forcing him to complete the morning’s remaining tests with significantly reduced aero.

However, reinforcing the fact that the WRC’s future looks bright, he and co-driver Enni Mälkönen went on to win the Ruuhimäki stage in the afternoon – their first fastest time at the sport’s top level, coming just a fortnight after fellow Rally1 rookie Mārtiņš Sesks achieved a similar feat in Latvia.

Grégoire Munster is seventh in his Puma ahead of FIA WRC2 leader Oliver Solberg, with category rivals Jari-Matti Latvala and top FIA WRC Challenger Robert Virves completing the top 10. Petr Borodin leads FIA WRC3 and FIA Junior WRC.

Saturday is the rally’s longest leg and features 144.22 kilometres against the clock, including the return of the legendary Ouninpohja stage.