Three wins in their last four had put early pacesetters Assat back into the conversation for top-four qualification, but their recent form came under pressure midway through the first period when Tomas Mazura gave KooKoo the lead.
Things got better for the visitors just 41 seconds into the second period, as Santeri Sulku doubled their lead, but the Pori side hit back within a minute, as Jonne Tammela reduced the deficit to 2-1.
A hooking call against Johan Olofsson hindered Assat's chances of turning the game around, as Ville Meskanen took full advantage to score on the resulting powerplay, but soon it was KooKoo gifting chances, as Kalle Loponen was sent to the box for slashing and Olofsson made amends with a powerplay goal of his own.
Crucially, KooKoo deflated the Assat comeback hopes within seconds of the end of period two, as Oskari Luoto registered his second assist of the game, playing a role in setting up Jesper Ahlroth to make it 4-2.
Assat's fading chances were put to bed through their own poor discipline once again, as Sakari Kostilainen was penalised for unsportsmanlike conduct, and with four-and-a-half minutes to play, Veeti Miettinen notched another powerplay goal to round off a 5-2 victory for KooKoo.
The Kuovola side move into fourth, only goal difference ahead of Ilves, who occupied the same spot for 24 hours. Assat remain in eighth, still five points behind tonight's opponents.
Also this evening, Pelicans extended their winning run to four matches - currently the longest active streak in the Liiga - and moved into 12th with a 3-2 overtime victory away at Karpat.
The Lahti side kept their run going in dramatic fashion, as Roni Karvinen levelled the scores at 2-2 in the final minute of regulation, before Daniel Nieminen grabbed the winner in the third minute of OT, condemning 15th-placed Karpat to a second defeat in succession.
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