Hammarby's win over Brommapojkarna the previous day had seen the gap at the top close to five points, but Sirius made the perfect response by recording their second victory and clean sheet in a row following their three-game losing run.
Degerfors beat basement-dwellers Halmstad last time out and needed just a point to climb out of the bottom three, yet if all the pressure was on Sirius, it didn't show, as the home side needed only 76 seconds to go ahead.
Zalan Vancsa got free on the right wing and played the ball across goal, forcing backtracking defender Ahmad Faqa to turn the ball into his own net.
Having made the perfect start, the Uppsala side added some breathing space just before half-time, when Marcus Lindberg squared to Melker Heier, who took matters into his own hands, making a direct run into the box before arrowing a finish into the net which gave the goalkeeper no chance.
Both sides generated opportunities in the second half, but Degerfors failed to change the balance of the game, thus two goals were enough for Sirius to edge a step closer to the title, with nine rounds still to play.
Hammarby's victory had also seen them take second place back from Djurgarden, but their fellow 3Arena tennants responded with victory over GAIS that made them Sirius' closest challengers once again, in a match which saw both sides receive a red card.
There were 10 minutes left in the first half when the home side went in front - Bo Hegland curled a cross into the box which was perfect for Kristian Lien to volley in at the back post for his 16th of the season, making him the outright top scorer in Allsvenskan.
Just before the hour mark, Oskar Agren gave the ball away to Hegland and brought him down in an attempt to atone for his mistake. The referee deemed he was the last man, and showed Agren a straight red card.
It took just five minutes for Blaranderna to make the man-advantage count, as the Mackerels again gave the ball away sloppily, this time to Lien, who ran through on goal before returning the favour by squaring to Hegland, who tapped into the empty net.
Four minutes from time, Christos Almyras was sent off for kicking out at Henry Sletsjoe as tempers boiled over, but that did nothing to stop Djurgarden taking a fifth win in a row that takes them a point above Hammarby and seven clear of those outside the European places. GAIS sit 10th having taken one point from their last two.
Follow the Allsvenskan title race on Flashscore.