Unbeaten Sirius were looking for a second win in a row and an 11th of the season, but for a long time it looked to be 13th match unlucky for the visitors from Uppsala, who failed to breakthrough in the first half, even after Rasmus Wikstrom hauled Robbie Ure over inside the box - Isak Bjerkebo's tame penalty was saved by Isak Pettersson.
But Bjerkebo made amends eight minutes from time, when his corner was perfect for Mohamed Soumah to loop over Pettersson to finally give Sirius the lead. Bjerkebo wasn't done there - two minutes later, he went on a wonderful run down the left wing from inside his own helf before cutting inside and shooting, Pettersson was equal to it, but Ure followed in to score his 13th of the season.
Oscar Krusnell then gave the home side hope by turning the ball into his own net in the 88th minute, only for Sebastian Holmen to slip in midfield, and that was all the invitation Ure needed to race away and settle the tie with his 14th, and his seventh in July alone.
For Elfsborg, three defeats in a row coming immediately after four consecutive draws leaves them in ninth, albeit just five points off the European places they were recently among.
Hammarby ensured Sirius' lead did not reach double figures thanks to a comfortable win at home to Degerfors - a third win in a row since the summer break for the hosts, and a third loss in a row for the visitors.
The opener arrived late in the first half when a Victor Lind shot was parried straight to Paulos Abraham, who tucked away the rebound. Bajen put Degerfors to the sword with three goals in six second-half minutes, the first of which arrived with just over 20 minutes to go as Montader Madjed played a one-two with Lind before finishing in style.
The third arrived soon after as Hammarby players were queuing up to finish a ball into the box before finally Markus Karlsson set it back for Tesfaldet Tekie to curl into the top corner from 25 yards, then Madjed added his second with another curling effort from just outside the area.
Goteborg's win earlier in the round means Degerfors are now in the bottom three and without a win in nine in the league.
Degerfors are at least two places and four points clear of Halmstad, who were beaten for the fourth game in a row. Hacken were the victors to keep pace with Hammarby, staying three points behind with a game in hand, albeit with a vastly inferior goal difference.
It took almost 50 minutes to break the deadlock, but when Gustav Lindgren played the ball out to Mikkel Rygaard, he continued his run into the box to poke Rygaard's cross into the bottom corner.
Hacken and Lindgren only had to wait seven more minutes for a second, as Brice Wembangomo's low centre from the right put the ball on a plate for the striker to complete his brace and see Hacken return to winning ways after successive defeats.