Halmstad went into the international break with renewed survival hope after victory over AIK, but that hope has been dented again by Elfsborg, who strolled to a third consecutive victory that takes them to within three points of third-placed Hammarby.
The deadlock was broken as early as the third minute, when Leo Ostman got in behind and pulled the ball back for Momoh Kamara, whose first-time hit beat the goalkeeper at the near post. The second arrived with three minutes of the half left, this time Arber Zeneli was afforded space on the left and his low cross was diverted into his own net by Pascar Gregor.
HBK reached the hour mark without their evening worsening, but no further, as Niklas Hult did well to dig out a cross - again from the left side - and Ostman powered it home with his head. It was 4-0 with 12 minutes to play, as Elfsborg opened up the Halmstad defence with slick passing before Alexander Jensen - this time from the right - drilled a low ball across and Ostman applied the simple finish to make it a brace.
It's one league defeat in nine for the Boras side, while Halmstad are six points from guaranteed safety.
Halmstad are still just five points from the relegation play-off spot as Kalmar suffered a fifth successive Allsvenskan defeat, going down by the odd goal to Malmo, who returned to winning ways to go sixth, seven points off the European places.
The visitors created plenty of opportunities, but nothing was going right for Vilmer Tyren, who missed three big chances for KFF, and another bad day at the office for the strugglers was confirmed with 18 minutes to play, when Jens Stryger's clever backheel was taken down and turned home by Otto Rosengren for the game's only goal.
It's just one defeat in five in the league for MFF, while Kalmar are nine league games without a win as their slide continues.