The Hyundai Shell Mobis World Rally Team driver stopped the clocks at 2min 06.7sec on the 2.58km mixed-surface test in central Jyväskylä, beating team-mate Thierry Neuville by 1.1sec.
Championship leader Elfyn Evans and Sébastien Ogier shared third place, both completing the narrow and technical stage 1.2sec behind Fourmaux, while only 3.3sec separated the leading nine Rally1 crews.
Fourmaux had already shown his speed by finishing second on Thursday morning’s shakedown and delivered when the competitive action began, finding three seconds over the benchmark previously set by Hyundai team-mate Esapekka Lappi.
“I really tried to optimise everything,” Fourmaux explained. “I remember last year that the gaps were so tight on the long stages and we were losing more on the short stages, so I tried.”
Neuville completed a strong opening evening for Hyundai and was encouraged by the feeling aboard his i20 N Rally1 ahead of Friday’s high-speed forest stages.
“I’m always hungry,” said the Belgian. “It is not an easy one to win, but let’s try. The feeling is good in the car. There are a lot of new stages and it is probably the fastest Rally Finland I have ever seen.”
Evans made a solid start despite facing the prospect of sweeping loose gravel from the road as the opening car on Friday. The Welshman warned that the recent dry weather could make his task more difficult.
“It is probably not going to be ideal as it has been a bit too dry,” he admitted. “It is what it is. We have to get on with it the best we can.”
Ogier matched Evans on his first competitive stage since being reunited with former co-driver Julien Ingrassia, who was called up to replace Vincent Landais for this weekend.
“I’m pleased that Julien is there with me for one more time,” Ogier said. “All week we will have Vincent in the car with us. We will try our best.”
Takamoto Katsuta, fastest at shakedown, ended Thursday fifth overall and 1.8sec from the lead. Home favourite Sami Pajari followed one-tenth further back after describing Harju as “a really special” but difficult stage on which to find time.
Oliver Solberg took seventh after reporting understeer and several small mistakes, while Lappi, Jon Armstrong and WRC2 leader Robert Virves completed the top 10.
Friday brings the first full day of competition, with two loops of Laukaa, Saarikas, Sydänmaa and Hoho totalling 127.94 competitive kilometres.