Assat blew a two-game lead before ultimately getting over the line against Kiekko-Espoo, and they looked to be in for another serious test when they went a goal down on the road against SaiPa, as Juuso Heikkila grabbed the series' opening goal in the 13th minute.
But the Pori side were level again when Sakari Kostilainen picked up a loose puck in his own zone seven minutes into the second period, carried it on his own and beat the goaltender.
A tripping call against Aleksi Anttalainen soon after allowed SaiPa to retake the lead through Antti Kalapudas on the powerplay, only for the hosts to be penalised for too many men on the ice, and Valtteri Lipiainen hit back with a powerplay goal for Assat to make it 2-2.
A goalless third period - which saw Santari Airola twice sent to the box - sent the match to overtime. This time, both sides were guilty of too many men on the ice, but neither could profit, as time ticked on and on with neither side able to find a winner in 20 extra minutes.
In the second OT period, neither high-sticking from the hosts' Otto Kivenmaki nor delay of game by the visitors' Nestor Noiva were punished on the resulting powerplays, and still the all-important fifth goal failed to materialise.
The match looked to have finally ended a whole 52 minutes 21 seconds into overtime when Feetu Knihti found the net, only to see his goal disallowed, and the game continued. Ultimately, the third period of overtime finished without a winner, meaning OT would last longer than regulation time.
With 64:23 on the overtime clock, the match finally had its decisive conclusion. A long clearance down the ice was picked up by Jan Mikael Jarvinen, he squared to Kostilainen, who somehow mustered the energy to power the puck past Tomi Karhunen to win it for Assat, 3-2, with his second of the game.
The Aces go 1-0 up in the series, with the prospect of six more matches between these sides almost too much to bear! In total, there were 110 shots on goal in the match, 65 of which were by the defeated hosts.
There were 35 shots on goal and two powerplays each in 60 minutes of hockey as KooKoo welcomed Pelicans for game one of their series, but amazingly, there were no goals.
The Lahti side had won 1-0 away at JYP to seal victory in their wildcard series after just three games, so the 11th seeds holding out on the road against the second seeds perhaps wasn't quite a surprise.
The Kouvola crowd were wondering if they were ever going to see a goal, and though overtime wasn't nearly as long as at SaiPa, it didn't go their way, as but with 12:57 played in the extra period, Johannes Johannesen scored the winner for Pelicans after Oskars Batna's set up
Patrik Bartosak made 28 saves for his second shutout in as many matches.
The other quarter-final tie to get underway today saw first seeds Tappara take on 12th and final seeds Hameenlinna, and the regular season champions were made to work for their narrow 2-1 home win.
Henrik Haapala's goal in the eighth minute put the Tampere side in front, but on a three-match run having knocked out Lukko in the wildcard round, HPK showed again they were no pushovers, levelling with four minutes left in the second period through Elmeri Eronen.
Less than a minute later, Garrett Pyke was dismissed for cross-checking, and it was on that penalty that the game swung, as Kasper Simontaival scored on the powerplay with just seven seconds to play in the period, before the Battle Axe held on through a goalless final 20 minutes.
The fourth quarter-final between Ilves and KalPa gets underway on Sunday 29th, with game two of HPK vs Tappara and Pelicans vs KooKoo taking place on Monday 30th. Assat and SaiPa will be more than grateful to have an extra day's rest, back on the ice on Tuesday 31st.