KooKoo had built some momentum with back-to-back wins against Hameenlinna, but travelling to the league leaders was expected to be a much tougher test.
However, the only surprise was that the visitors weren't ahead and clear after 40 minutes, in which time they had 33 shots on goal to Assat's 12, but home goaltender Jan Bednar was single-handedly keeping the match goalless.
But his resistance was finally broken in the 15th minute of the final period, when Jimi Suomi put KooKoo in front. Having waited so long for one, the Kouvola side grabbed their second goal a little over a minute later, through Akseli Makinen.
Assat rallied late on, and Miro Karjalainen pulled one back despite being shorthanded, but it wasn't enough for the hosts, who fell to a second defeat in four with the 2-1 loss. It's three wins in a row now for KooKoo, who are in ninth place - top of the bottom half.
Assat can consider themselves fortunate that their lead has only been cut by a point, as JYP were defeated 5-4 after penalties against struggling Karpat.
Two from Arttu Alasiurua and one from Eemil Erholtz put Karpat 3-2 ahead after 20 minutes, and after a goal apiece in the second, Leevi Tukiainen's strike nine minutes into the third period levelled the scores at 4-4 and took the sides to overtime, which finished goalless.
Neither side could score their first three penalties, before Patrik Virta converted for the visitors, which meant Pekka Jormakka had to score for JYP, but he could not find the net, meaning Karpat ended a run of only one win in seven.
JYP's five-match winning streak comes to an end, which means they are now three points behind Assat, but with a game in hand.
Tappara moved up to third as a comfortable 4-1 win over IFK Helsinki marked the first time they have picked up back-to-back victories in a month. The bottom side, meanwhile, saw their losing run extend to six matches.
Dropping back to fourth place are Kiekko-Espoo, who fell to an Alberts Smits goal 35 seconds into overtime that gave Jukurit the 3-2 win that keeps them in seventh, one point behind tonight's opponents, who have now lost two in three.
Also picking up a 3-2 overtime win were Lukko, who are level on 31 points with Jukurit but are ahead on goal difference, after Alex Beaucage notched the winning goal in the third minute of the extra period to see off Vaasan Sport.
Sport slip into the bottom two by virtue of their loss and Pelicans coming from behind after one period to take a convincing 5-2 win at home to Hameenlinna. It's a first win in four for the Lahti side, while the visitors have seen their losing run stretch to four.
Finally, SaiPa registered just a second win in six by wrapping up a 5-2 win over a dogged Ilves side. It's successive losses now for the Tampere side after their recent good spell, they stay just outside the Playoff places, while SaiPa are now one of four sides just a point outside the top four.