Not only had Sirius lost three in a row, they were winless in four since Robbie Ure departed, and that run looked set to continue after a goalless first half in which Isak Bjerkebo had the best chance but was unable to poke the ball past the goalkeeper.
But early in the second half, the Uppsala side made the breakthrough, as Zalan Vancsa's cross from the right took a deflection, but that only helped the ball fall perfectly for Jesper Uneken, whose powerful header sailed into the top corner - the first Sirius goal for the man brought in to replace Ure.
Crowd trouble forced the referee to halt the match for over 20 minutes, but Sirius didn't let the wait or the disturbance get to them, as they held on for a precious three points that takes them nine clear of Hammarby for the time being. A first loss in three for Vasteras sees them sit in eighth place.
Degerfors remain in the relegation play-off place but victory to end a two-game losing run has pulled them five points clear of the bottom two, as opponents Halmstad remain bottom of the pile as their two-game unbeaten run came to an end in untimely fashion.
A double substitution in the 69th minute turned the game, as the hosts brought on Ludvig Fritzson and Nahom Girmai. Seven minutes later, Dikan Vukojevic slotted the ball through to Fritzson, who held his nerve to guide the ball into the bottom corner.
Two minutes from time, the points were sealed when Elias Barsoum went on a long run from inside his own half before picking out the run of Girmai, and the Eritrean coolly clipped the ball over the goalkeeper.
Only goal difference Degerfors and Kalmar above them, while Halmstad are eight points from that 13th and final guaranteed survival position.
Djurgarden's victory over Mjallby meant Hacken were unable to reclaim third place in this round, but they were unable to keep pace with the Stockholm side after a goalless draw at GAIS in a Gothenburg derby.
The visitors failed to make the most of first-half chances, as Gustav Lindgren side-footed a shot too close to goalkeeper Mergim Krasniqi from right in front, before Adrian Svanback drilled a low effort from outside the area, but Krasniqi got down well to deny him.
In the second half, Hacken were hanging on for a point and had their goalkeeper, Etrit Berisha, to thank for a superb double save, denying Max Andersson before getting back up and making himself big to smother Nikola Vasic's rebound.
Hacken are fourth, three points behind Djurgarden with a far inferior goal difference, and are now winless in two. GAIS sit ninth after taking four points and back-to-back clean sheets from their last two.
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