Hammarby had acquired a reassuring 3-1 lead in the second half after, among other things, two goals by Gustav Ludwigson.
Then Oliver Berg created nerves in the match when he reduced it to 3-2 with 20 minutes left to play.
Berg grinned evilly after the goal, when his leg tasted Bajen goalkeeper Oliver Dovin's studs in the melee, but continued to play as the motivation was greater than the pain.
But then came the death blow for the guests.
Hammarby was responsible for a pattern attack, Nilsson to Sandberg who shot the cross aimed at Luwigson, but which instead turned into an own goal when Kalmar's Axel Lindahl cleared by shooting the ball into his own box.
Hammarby's victory means that the team is basically ready for the European Games.
Bajen are three points ahead of AIK with one round to play, but with a significantly better goal difference than their northern Stockholm rival.