It is three wins on the spin now for Skelleftea, who comprehensively beat Farjestad 6-2 to go 3-1 up in their series.
Farjestad conceded three penalties in the first period, and each time the home side took advantage with powerplay goals courtesy of Michael Brandsegg-Nygard, Par Lindholm and Max Lindholm.
The second period was a better one for the visitors, although it took them until the final minute to break through, as Axel Bergkvist made it 3-1.
But the Black & Yellows did not let it get to them, and they needed less than three minutes to restore the three-goal cushion through Oskar Vuollet.
Though Joackim Nygard made it 4-2, once again ill-discipline cost the Karlstad club - Viktor Lodin received a game misconduct penalty for cross-checking, allowing Vuollet and Anton Heikkinen to capitalise.
Skelleftea have the chance to seal their Quarter-Final place on Saturday at Löfbergs Arena in game five.
The series between Timra and Frolunda is guaranteed to go to at least game six after the former secured a crucial 2-1 victory on home ice to level matters at two wins apiece.
An overtime loss at the SCA Arena in game three meant Timra had to win or give the Gothenburg club the chance to wrap up the series at the Scandinavium in game five.
The first period was scoreless and powerplay-free, but the match came to life six minutes into the second period when the home side were awarded a penalty shot.
Magnus Paajarvi held his nerve to beat Tobias Normann and break the deadlock.
Timra seemed to be edging to the tightest of victories, until midway through the final period - Paajarvi was the guilty man this time, penalised for holding, and Arttu Ruotsalainen found an equaliser for Frolunda on the powerplay.
Another overtime period between these two looked to be on the cards until three minutes left when it was Timra's turn to have the man advantage - and take advantage - Emil Pettersson fired home what could be a pivotal goal in their season.
Game five in Gothenburg is also set for Saturday.