Björklöven got off to a dream start when Francis Perron sent in an early lead goal.
In the second period, they also increased to 2-0 after a free kick where Gustav Possler served Olle Liss.
But Karlskoga got up and came back.
Henrik Björklund's two goals meant that they had a 2-3 deficit when the second period was over.
And in the third period, Linus Karlsson fixed the equalizer that took the match to extra time.
A nice revenge after the carelessly beaten pass that caused Björklöven's 2-0 goal.
- I have to admit that we were down 0-2.
I'm absolutely horrible.
It is the worst effort of the season for me, a self-critical Karlsson told C More during the break.
The extension was a dramatic long run.
It was only in the third overtime period that Gustaf Franzén was able to make the match decision.
Thus, Karlskrona has connected the grip on the semifinal series.
The next match is played on Tuesday.
For club icon Carl Berglund, the evening was not as fun.
The Karlskoga player, who was celebrated for having passed 600 matches in the club, had to go to hospital after receiving a puck in the head.
- We do not take chances on such things.
We pick him up and we will evaluate the situation tomorrow, says club manager Torsten Yngvesson in C More.
Carl Persson was hit by a puck and had to go to hospital.
Photo: Bildbyrån