After two one-goal wins and needing overtime in game two, Assat wrapped things up in style, recording a 5-1 win.
Nestor Noiva broke the deadlock in the 12th minute and the home crowd in Pori thought they were in for another tense evening, as no goals followed in the rest of the first period.
That all changed midway through the second, when Valtteri Viljanen doubled the lead after Assat survived two Hameenlinna powerplays, before Jan-Mikael Jarvinen made it 3-0 when the hosts had a man advantage.
Noiva scored his second to put the match beyond doubt, and though Sami Paivarinta pulled one back, the visitors' meagre hopes were dashed when Rami Maatta found the empty net.
Assat will have the chance to rest before they start their Quarter-Final series with Ilves.
Having gone down twice to lowest seeds TPS Turku, SaiPa pulled a win out of the bag when they needed it most, running out 3-0 victors to cut TPS' lead in the series to 2-1.
Otto Salin was the TPS hero in the first game, but it was a slashing call against him in the opening minutes that allowed SaiPa to break the deadlock on the powerplay, through Antti Kalapudas.
Having survived penalties of their own, Samuli Niinisaari doubled the Lappeenranta side's advantage in the final minute of the first.
Late on, Mark Pysyk scored for the second match running, but this time to secure the win with an empty-net goal, before tempers boiled over at the end of the game, ending with Turku's Oliver Lauridsen being ejected.
In Espoo, the home side on the night took the win for the third time in this series, as Kiekko-Espoo beat Tappara 5-2, putting the reigning champions on the brink of elimination.
Thrashed 6-1 two nights ago, K-Espoo ensured there would be no repeat as Heikki Liedes, Santeri Virtanen and Tobias Ekberg put them 3-0 up after 11:25.
The second period belonged to the visitors, as Philip Granath and Julius Mattila reduced the gap to one, but hopes of completing the comeback were dashed in the third when Peter Quenneville scored with less than four minutes remaining.
Liedes scored his second of the game into an empty net, to complete the three-goal win.
Having been pegged back in game two, Vaasan Sport have gone ahead in the series again with a 2-1 win away at KooKoo.
Seth Barton picked up an assist in KooKoo's 3-0 win in game two, and tonight he wasted no time in going one better, scoring after just 50 seconds.
However, the seventh minute of both the second and third periods were the home side's undoing, as Lari Heikkinen equalised before Cole Fonstad completed the turnaround.
In contrast to the series between K-Espoo and Tappara, the away team has picked up all three wins thus far.
Sport will host game four tomorrow, which also sees TPS and Tappara on home ice in their respective matches.
Pelicans draw first Playout blood
Tonight also saw the the first game in the best-of-seven Playout series, as the bottom two teams from the regular season look to maintain their place in the Liiga.
Pelicans finished 26 points clear of Jukurit over 60 matches, so it was little surprise that they secured a win on home ice.
The more surprising factor was that they laboured to a 2-1 win.
Two Antti Tyrvainen goals had put them 2-0 by the ninth minute of the second period, but failing to kill the game off allowed Jesper Piitulainen to set up a grandstand finish in the closing stages.
Jukurit thought they had forced overtime with 40 seconds to play, only for Sakke Hamalainen's goal to be ruled out following a video review.
Game two of the Playout also takes place tomorrow.