Inter Turku's victory over KuPS in the top-of-the-table clash the previous day had given HJK the chance to grab second place on goal difference, and it's a chance they took with a second victory in a row, but only surviving a late rally against AC Oulu, who have lost four from five in the Championship group.
By half-time, the visitors seemed to be coasting to victory, as Leonel Montano set up Mads Borchers to score after 20 minutes, then with the break approaching, Borchers turned provider for Liam Moller to make it 2-0.
Camilo Triana struck for the hosts early in the second half but HJK rolled out the Montano-Borchers combination again, as the latter completed his brace with just over a quarter of the match to play.
But the HJK lead fell apart in the space of seven minutes, courtesy of Rasmus Karjalainen, who first found Roope Riski to make it a one goal game, and then set up Mikko Pitkanen to equalise in the 84th minute.
However, the Helsinki side weren't going to miss this particular opportunity, and just two minutes later they were back in front when Santeri Haarala's shot was saved, but diverted into the path of Joona Veteli, who fired home the rebound.
HJK are now unbeaten in six matches, while Oulu failed to build on their victory over KuPS in their previous fixture and drop to sixth place.
It's not all bad for news for Oulu as they are still just five points off the European places thanks to VPS' win over Gnistan, a result that puts just three points between the pair.
The only goal arrived in the final 10 minutes of the first half, when Casper Holmelund dug out a cross from the left side and it was headed home in style by Xavier Odhiambo, his second goal for the club.
The Vaasa side held on to end their three-game losing run, while Gnistan remained 10 points off top spot thanks to a first defeat in nine matches.