It's three defeats and a draw in their last four league outings for KuPS, who have failed to score in any of those matches. They went behind in this one just past the half-hour mark, as Anton Popovitch headed home from a corner.
Before the break, it was 2-0 courtesy of a Jardell Kanga penalty, then Adeleke Akinyemi completed the scoring early in the second half when latching onto a Kanga through ball.
The victory takes Ilves to four matches unbeaten and 22 points, one shy of KuPS but with a game in hand.
The Tampere side have overtaken Inter Turku, who are still unbeaten but missed the chance to go top with a 1-1 draw at home to Haka.
Bismark Ampofo set Inter onto what they hoped would be a fourth consecutive win inside the first 15 minutes, only for Simon Lindholm to grab an equaliser early in the second half.
Only goal difference is separating Ilves and Inter, while Haka have dropped a place to eighth despite a third game unbeaten.
Now within just three points of first place are HJK, who made light work of their away trip to bottom side AC Oulu, winning 4-0.
Benji Michel got the ball rolling midway through the first half, before the Helsinki side caught Oulu on the counterattack with 20 minutes to go, resulting in Teemu Pukki setting up Alexander Ring to double the lead.
Liam Moller went round the goalkeeper and laid number three on a plate for Georgios Kanellopoulos, then Michael Boamah completed the rout in added time.
After seven Veikkausliiga matches without a victory, SJK picked up a much-needed three points by beating Jaro 3-1 at home to stay fifth, while the visitors slip to five without a league win.
Rasmus Karjalainen tucked away a penalty for the hosts in the 11th minute, before Kasper Paananen secured some breathing space inside the first half an hour.
Kerfala Cissoko set up a nervy finish when he pulled one back three minutes from time, only for Jeremiah Streng to re-establish the two-goal cushion in the final seconds.
Only three points separated VPS and Mariehamn before kick-off in their meeting, but there was a gulf in class between the two on the pitch, as VPS ran out 5-1 winners away from home.
Olli Jakonen scored the only goal of the first half, then Maissa Fall and Jakonen again put VPS in full control. Prosper Ahiabu made it 4-0 and though Emmanuel Okereke grabbed a consolation for Mariehamn, there was still time for Fall to complete his brace late on.
VPS stay sixth, while Mariehamn remain ninth despite their goal difference taking a hit.
Finally, two goals from Joakim Latonen earned Gnistan a 2-1 win over KTP in Helsinki.
The visitors went ahead in the first half through Petteri Forsell, only for Latonen to strike in the 65th and 92nd minutes to complete the comeback. Gnistan climb to seventh, whilt KTP remain one point off the foot of the table.