A 2-1 win in Tampere on 9th May had given KooKoo the chance of winning a maiden Liiga title in front of their home crowd in Kouvola, knowing if they lost, Tappara would have home advantage in game seven.
Tappara gave the hosts the chance they were waiting for in the 14th minute, when Joni Tuulola was penalised for tripping. The visitors technically survived the powerplay, but following two minutes of being stretched they conceded five seconds after getting back to full strength.
Jimi Suomi squared the puck to Ville Puhakka, who powered an effort from the blue line through the crowd and into the net.
But with their ambitions of another title under serious threat, Tappara came out firing in the second period and took under three minutes to equalise. Tuulola's pass downfield was carried over the blue line by Joachim Blichfeld, who waited for the defence to commit before slamming home in style.
Slashing by Daniel Brickley soon after threatened to derail the Tappara fightback, but not only did they survive another powerplay, the visitors didn't let their guard down when back to full strength, and instead took the lead just after the midpoint of the match.
This time both Tuulolas combined for the assists - Joni found Eetu, who carried the puck behind the net before laying it back for Aapeli Rasanen to strike the Battle Axe ahead.
Interference against Ossi-Petteri Jaakola eight minutes into the third period did little to help the KooKoo comeback. The home side generated 12 shots on goal to Tappara's two in the final 20 minutes, but Christian Heljanko kept them out to secure a 2-1 victory.
All eyes now will be on Nokia Arena in two days time, where either Tappara will lift the Kanada-malja for the 21st time, or KooKoo will become Finnish champions for the very first time.
Follow the deciding match of the Liiga finals on Flashscore.