The Swedish football giant Halmstad would have been only two points behind Degerfors in the qualifying place with ten games left to play if they had won.
After the 2-0 loss in front of over 5,500 spectators at Stora Valla, the gap is instead eight points.
The decisive goal came with barely a quarter of an hour left to play when the Halmstad defence simply watched ball carrier Dejan Vukojevic, who was easily able to free scorer Ludvig Fritzson from deep.
In the 88th minute, Nahom Netabay secured the victory for the Värmland side at 2-0.
Halmstad has collected eleven points in 20 matches. Degerfors has 19 points.
The Gothenburg derby between Gais and Häcken ended goalless.
