Series leader Frölunda led 2-0 and 3-2 at home in Scandinavium, but did not manage to puncture the match during regular time.
Visiting Oskarshamn - who had two straight victories - equalized to 3-3 in games four against four at the beginning of the third period after Michael Spacek incurred match penalties for headbutting.
There were no more goals in the third and the match went to extra time, where Frölunda got the chance to decide in four against three with 31 seconds left after the guests' David Quenneville went out for a high club.
But Frölunda did not manage to manage the numerical superiority and instead Oskarshamn went home with the extra points after penalties.
The text is updated.