Gnistan caused the shock of the season so far last time out, winning away at Helsinki neighbours HJK, but they could not pull off a similar surprise at home on Sunday, losing 2-1 to the holders.
For a while, another giant-killing was on the cards, as they led at half-time thanks to Gabriel Europaeus' goal after 28 minutes, which he curled into the top corner from just inside the penalty area with aplomb.
That goal came against the run of play, with the Oulunkyla side surviving their woodwork being struck and needing a plethora of saves and goal-line clearances to stay in the game.
It was perhaps inevitable that KuPS would eventually find a way through, and the equaliser came in the second minute of the second half thanks to Jaakko Oksanen, who guided the ball into the bottom corner with a clean strike from the edge of the area.
13 minutes from time, Gnistan hearts were broken by Petteri Pennanen, whose side-footed shot lacked power, but found its way through a crowded penalty area and into the back of the net.
It's four wins in a row now for KuPS after they began the campaign with a draw, while the three points against HJK remain Gnistan's total for the season so far.
SJK had the opportunity to return to the top of the table 24 hours later, but they failed to capitalise and were instead held 2-2 by Haka.
They looked set for a fifth win in a row after 21 minutes, when Alenis Vargas' 30-yard strike flew into the top corner to put the home team ahead.
The Seinajoki side doubled their lead 14 minutes from time thanks to Jeremiah Streng, who beat the offside trap and raced away to slot home.
With 90 minutes on the clock, Haka grabbed what appeared to be no more than a consolation when a low cross was turned in at the back post by Jordan Houston.
It wasn't Houston, but SJK, who had a problem six minutes into added time, as Haka completed an unlikely late comeback, courtesy of Kalle Multanen, who emerged within a crowded penalty area to bundle a corner over the line.
The capitulation means SJK now trail KuPS on goal difference, while Haka now have seven points from four matches.
HJK's disastrous three-match losing start to the season was ended at the weekend, as they won 3-1 to inflict successive losses on VPS.
A return to winning ways was marked by the first Veikkausliiga goal for Teemu Pukki since his return to his homeland, scoring from the penalty spot after four minutes.
Pyry Mentu settled the home side's nerves further with a goal in first half stoppage time, and though Alife Cicale pulled one back after the hour mark, Benji Michel wrapped things up for the record champions two minutes from time.
Ilves have dropped to fourth after their perfect start was ended by Mariehamn, who move into the top half with a 3-2 home win.
The Lynx's cause was not helped by a red card shown to Otso Virtanen with only four minutes on the clock, allowing Mariehamn to build a 2-0 lead at the break courtesy of Sebastian Dahlstrom and Niilo Kujasalo.
But the 10 men hit back after half-time through Joona Veteli and then Matias Rale, who made it 2-2 at the hour mark. However, the Tampere side were back level for a matter of seconds, as Muhamed Olawale scored what turned out to be the winner.
Also reduced to 10 men were AC Oulu, who stay bottom of the table and without a point after a 4-1 home loss to Inter Turku, who move third and stay unbeaten.
Julius Paananen gave the strugglers an early lead, but goals from Mamodou Sarr and Jasse Tuominen before the break meant the match began to follow the form book.
William Eskelinen's red card all but ended Oulu's hopes, before Axel Kouame and Thomas Lahdensuo completed the scoring in the final 10 minutes.
A first win of the season for KTP has seen them move up to eighth, a place ahead of Jaro, who they defeated 3-2 on the road.
The visitors had twice taken the lead either side of half-time, but put daylight between themselves and the league's new boys with a Tabi Manga penalty 16 minutes from the end.
Kerfala Cissoko scored his fourth of the season to set up a grandstand finish, but it wasn't enough to prevent Jaro from falling to a third defeat in a row.