After three consecutive wins, a 3-2 loss at KuPS in midweek did little to dampen AC Oulu's impressive start to the season, but the same cannot be said for this defeat, as Lahti picked up their first points since the opening day.
Lahti took all of five minutes to take the lead, when a clipped cross to the six-yard box was headed only as far as Martim Augusto, who powered a sweet right-foot volley into the net from 12 yards out.
Across the rest of the half Oulu had chances to equalise, and thought they had done just that in the 45th minute when a Julius Korkko strike was controversially ruled out for offside, and a bad few minutes for Oulu got worse when Neemias nodded in Romain Sans' corner three minutes later.
The visitors got the goal the perhaps merited midway through the second half when neat build-up in the attacking third resulted in Rasmus Karjalainen finding Korkko at the edge of the box, and this time his 20-yard screamer would not be disallowed.
But that was not enough for Oulu, who lose back-to-back games - a run that Lahti have just ended, they sit sixth with six points so far.
Inter Turku scored a third win in a row and are now only behind leaders KuPS on goal difference after a narrow win over Mariehamn, who remain winless in 10th having drawn their home matches and lost their away.
The trip to Turku appeared to be too much for them in the first half, as the home side had 10 shots to their one, but FC Inter were being wasteful with their opportunities and it was goalless after 45 minutes.
It looked to be a frustrating afternoon for the hosts, until 12 minutes from time, when Jussi Niska's floated cross to the back post was nodded down by Alie Conteh, and his header managed to squeeze through the gap between the near post and the goalkeeper to give the Turku side the points.