Finland's current champions ensured they left Helsinki with the bragging rights after thrashing Finland's record champions in a result that takes KuPS top on goal difference and ends HJK's four-match unbeaten run.
The key moment of the contest came just 12 minutes in, when Ville Tikkanen was given a straight red card for handling the ball. A harsh punishment in normal circumstances, but in using his arm to divert a ball over the top, the defender denied a clear goalscoring opportunity for Jaime Moreno, who was looking to run in behind.
The 10 men managed to keep the game tight for almost half an hour, but four minutes before half-time, KuPS found a way through when Petteri Pennanen took aim from 25 yards and his strike flew past Jesse Ost. Eight minutes into the second half, Pennanen was at it again, picking up a loose ball at the edge of the area following a swift attack, and coolly burying the chance for his third goal this week.
HJK managed to stem the tide, but only for so long, conceding twice more in the final 11 minutes; Moreno's excellent run into the box had KuPS players queuing up to finish, but it was Moreno who finally headed home Taneli Hamalainen's cross. Arttu Heinonen made it four soon after, tapping home after Ost had fumbled a cross.
Those two late goals were crucial for the Kuopio side, improving their goal difference to +12, one better than Inter Turku's, with the sides level on 30 points. HJK stay fourth but are now eight points behind.
Inter Turku finally put their run of four successive draws behind them, but their lack of wins came back to bite them, as KuPS' superior goal difference knocked them back to second. Alie Conteh pounced on a loose ball in first half added time to break the deadlock, before completing his brace with another late strike, making it 2-0 in the 95th minute. FC Inter are unbeaten in 12 in all competitions, while Mariehamn have lost five straight in the league.
TPS put a three-game winless run behind them by winning a thriller at home to Jaro. Albijon Muzaci's early opener for the hosts was replied to with two Herman Sjogrell goals before the break, but hopes of just a second win of the season for the visitors were dashed by a Timo Zaal equaliser early in the second half, before Muzaci struck again in the 91st minute to take the points and keep TPS in seventh place.
SJK staged a late comeback to earn a second successive draw away at Ilves, who will be frustrated to have taken just one point from their last two. The hosts had two penalties in the first 11 minutes of the second half, and Jardell Kanga scored both to go top of the league's scoring charts with eight. But strikes from Samuel Chukwudi and Kasper Paananen - his third in his last four games - in the final eight minutes of the 90 earned a point. Ilves stay eighth and SJK two places further back.
There was nothing to separate the sides in sixth and fifth place, respectively, in the table, despite Gnistan taking a 20th minute lead when Adeleke Akinyemi bundled the ball in after a delightful Roman Eremenko pass in the build-up. VPS levelled 16 minutes later through Luka Smyth - a sixth of the season for the Australian. VPS stay two points clear, but it's Gnistan on the longer unbeaten run (5-4).
AC Oulu slipped to four points behind the top two, but it could have been worse had a Rasmus Karjalainen penalty not salvaged a draw in the 78th minute, shortly after Cristobal Montiel had given Lahti the lead. It's two without a win for Oulu and four for Lahti, who remain in ninth place.
Check out the Veikkausliiga results, stats and standings on Flashscore.