Inter Turku had Loic Essomba to thank for setting them on course for an 18th league match unbeaten this campaign; the Cameroonian set up Florian Krebs and then Jean Botue to put the visitors 2-0 up with 27 minutes played.
HJK got right back into contention with 20 minutes to go when Alex Ring made no mistake from the penalty spot, but Inter made sure of the points in the final five minutes.
Seth Saarinen drove in from the right wing and cut the ball back for Johannes Yli-Kokko to apply the side-footed finish. Then, in added time, Axel Kouame and Bismark Ampofo combined for the latter to make it 4-1 to the Turku side.
Following successive 4-1 wins, Inter have hit the 40-point mark with four matches of the regular season to play, while HJK are eight points further back after seeing their three-match winning run end.
Ilves may have lost touching distance with Inter but can take comfort from the fact their 2-2 draw at home to Gnistan confirmed their place in the Championship Round for this season.
Early on, not even a draw looked likely for the Lynx, as they fell behind with 10 minutes on the clock, courtesy of Saku Heiskanen, who forced his way through the defence before sneaking his shot in at the near post.
But the lead lasted only two minutes, as Teemu Hytonen cut inside and squeezed a strike through the legs of Gnistan goalkeeper Alexandro Craninx.
The Tampere side then completed the turnaround early in the second half through Marius Soderback, only for the visitors to force a share of the spoils 15 minutes from time, when Rachide Gnanou climbed highest at the back post to power home Heiskanen's corner.
That equaliser ended a two-match winning run for Gnistan, keeping them seventh but moving level on points with VPS, who occupy the sixth and final Championship Round place.
SJK stay fifth but are now 10 points clear of those outside the Championship Round places after they cruised to a 3-0 win over KTP.
Kasper Paananen broke the deadlock with 19 minutes on the clock, before the home side gave themselves some breathing space when Alenis Vargas made it 2-0 on the stroke of half-time.
Petteri Forsell wasted a huge chance to get his team back in the game from 12 yards just before the hour mark, as Roope Paunio guessed right to thwart his penalty.
The victory was wrapped up 17 minutes from time by Babacar Fati, whose cross-cum-shot evaded everyone and sneaked under the crossbar. The Seinajoki side bounced back strongly to defeat to Inter, while KTP remain bottom after a first loss in three fixtures.