With Ilves not in domestic action this midweek, Inter Turku knew a win would take them back to the top of the standings, but that looked no easy task against an SJK side defending a six-match unbeaten run in the league.
Inter, though, certainly made it look easy - they took the lead in the first minute of the match when an Axel Kouame strike from an impossible angle struck the post and rebounded for Dimitri Legbo to finish.
It was 2-0 to the hosts in the 27th minute, when Legbo's cross from the right found an unmarked Jean Botue, who made no mistake with his header.
SJK's defence had no answer to the relentless Turku attack, which carved their opponents open with seven minutes of the half to play - a brilliant one-touch move which began on the right wing ended with Florian Krebs feeding Kouame, who calmly side-footed the third goal home.
But the Seinajoki side gave themselves a glimmer of hope in first half stoppage time, when Samuel Chukwudi set up Kasper Paananen to make it 3-1 at the break.
However, the day clearly belonged to Inter, who finally put the icing on the cake in the 95th minute - Jasse Tuominen chased Kouame's ball over the top, rounded the advancing goalkeeper and rolled in the home side's fourth.
The win ensured Inter bounced back from a disappointing draw with KTP last time, and that they have qualified for the Championship Round with five regular season matches still to play. A first league loss in six sees SJK stay fifth, three points behind KuPS, who did not play this weekend.
On Monday, HJK took revenge for their defeat in the reverse fixture, winning the Helsinki derby 4-2 away at 10-man Gnistan to climb to third in the table, a point clear of last season's champions.
Gnistan's chances of a maiden league double over their neighbours was dealt a huge blow 21 minutes in, when Evgeniy Bashkirov was sent off. The 10 men held out for another 17 minutes, before Georgios Kanellopoulos set up Benji Michel to break the deadlock.
Nine minutes after the break Kanellopoulos got his second assist of the match, finding Santeri Hostikka, who cut inside and took a strike on from the edge of the area, which took a wicked deflection and trickled past the wrong-footed goalkeeper.
The home side made a game of it three minutes later, when Gabriel Europaeus pulled a goal back, only for HJK to restore their two-goal advantage with 25 minutes to play, courtesy of Michel's second of the match, nodding home Hostikka's cross.
Kai Meriluoto put the game beyond doubt soon after, and though Artur Atarah grabbed a consolation, it was job done and a third league win in a row for HJK, while Gnistan remain seventh after back-to-back losses.