The match in Jyvaskyla was more one-sided than the final score suggested, as a Leevi Tukiainen strike midway through the first period, and a powerplay goal from Valtteri Ojantakanen in the dying embers of the first put JYP 2-0 up.
Then, Tukiainen repeated his trick in the 13th minute of the second, before Daniel Torgersson all but sealed the win with over 23 minutes of the match to play.
Miska Siikonen and Marcus Davidsson added consolations for the visitors in the final two-and-a-half minutes to make it 4-2, but a third loss in a row is a real concern for KooKoo, especially after such a long winning run, while JYP are now two points ahead of them, earning a third win in four.
The rest of the night's focus was on the race to finish in the top 12, and Jukurit were the biggest winners, as they went 11th by ending a three-match losing streak thanks to a 4-0 win over Vaasan Sport.
Justin Addamo's goal early in the second was the only goal of the match until six minutes into the final period, when Jukurit began a scoring spree - Sakke Hamalainen, Jesper Piitulainen and Jiro Frilander all found the net in a little over three minutes to put the match to bed.
Evan Buitenhuis made 16 saves at the other end to complete his shutout, leaving the Vaasa side 10 points adrift at the bottom of the table.
That 10-point gap has been opened up by Karpat, who survived a late fightback from Kiekko-Espoo to win 4-3 at home and end their four-match losing run.
4-3 was also how things ended in the capital, as IFK Helsinki gained a sixth win in eight to move within a point of the Playoff places, while it's seven defeats in eight for Hameenlinna, who sit three points and one place further back.