Diego Garcia headed in Theodor Lundbergh's left-footed cross shortly before half-time. No more goals were scored at Studenternas, despite intense pressure from the home team in the second half.
With only one point taken in the last four Allsvenskan matches, the Uppsala club is losing its previously large lead.
With eleven rounds remaining, there is a six-point gap to Hammarby.
"Very heavy, of course. In the second half we do exactly what we have to. They defend well and unfortunately we don't get the ball in," Sirius striker Isak Bjerkebo tells TV4.
He agrees that there is a certain gold rush.
I think it's there subconsciously. It's completely normal. Everyone is human, but I don't think we see it on the pitch. We're as good as we can be in the second half, but we're not getting the ball in.
The match may have been the striker's last at the club for now. There has been speculation about a move abroad during the summer.
"There are a few hours left until the (transfer) window closes. We'll see then," he says.
Reigning Swedish champions Mjällby are still struggling and risk being dragged into the relegation battle if things don't turn around for the better.
Djurgården showed no mercy, winning at home 4–0 after leading 3–0 at halftime. Kristian Lien scored twice in the first half.
In connection with the match, Djurgården presented new signing Charlie Rosenqvist, 19, from Kalmar FF.
At home at Gamla Ullevi, Gais beat Brommapojkarna and won 4–0.
