Hammarby had picked up six points from their previous three league matches, which had all ended 3-2, but another goal-fest looked unlikely as they failed to break Norrkoping down in the first half despite dominating possession.
But the Bajen finally found a way through six minutes after the break - Nahir Besara failed to make a firm connection with Montader Madjed's cross, but with the second bite of the cherry he lashed the ball in on the volley.
The visitors kept the pressure on and made it count shortly after the hour mark. Again it was Madjed causing problems on the right and when his low cross was turned away to the edge of the penalty area, Ibrahima Fofana was on hand to power the ball through the crowd for 2-0.
Hammarby are now six matches unbeaten going into their crucial UEFA Conference League qualifying second leg against Rosenborg on Thursday. Successive losses for Norrkoping leaves them in 11th place.
What was a good weekend for the top two was a disastrous one for the chasing pack - after Malmo's loss to Mjallby, third-placed Elfsborg were held to a shock 2-2 draw at home to rock-bottom Varnamo.
The home side looked to be on course for a third win in a row when Leo Ostman gave them the half-time lead with a close-range header, only for the lead to be squandered when debutant Kai Meriluoto to steer in the equaliser just beyound the hour mark.
10 minutes later, Meriluoto's dream debut got better when Varnamo caught Elfsborg on the counter-attack, and the new man found Osto Liimatta, who unleashed a screamer into the top corner.
However, the home side got themselves out of trouble soon after, when Besfort Zeneli's beautiful ball in was glanced into the back of the net by Per Frick.
Elfsborg now find themselves 10 points behind Mjallby with 11 rounds of matches to be played. Successive 2-2 draws leaves Varnamo eight points from guaranteed safety.
Also losing ground in the title race were AIK, who are now three without a win after they were held to a goalless draw by local rivals Djurgarden on Sunday in front of over 45,000 fans in Solna.
The match was played at a great tempo, but the heroes at either end in the first half were the goalkeepers, AIK's Kristoffer Nordfeldt and Djurgarden's Jacob Rinne, who made three important stops apiece.
The chances kept coming in the second half, but the accuracy went missing - 20 shots in total eclipsed the total for the first half by some distance, but only three were goalbound and were all kept out by Nordfeldt.
The point at least takes AIK above Malmo into fourth, while the Iron Stoves remain seventh but go four unbeaten.
The other match on Monday saw a Gothenburg derby at the Gamla Ullevi, with GAIS playing hosts to their groundsharers, IFK Goteborg.
IFK broke the deadlock in the 12th minute after a cross from the left wing wasn't dealt with, allowing Saidou Alioum to play in Kolbeinn Thordarsson, who applied the finish.
A foul by goalkeeper Elis Bishesari gave GAIS the perfect chance to equalise eight minutes later, only for Ibrahim Diabate to blast the penalty over the bar.
1-0 was how it stayed, meaning not only have Goteborg earned local bragging rights and moved to within a point of GAIS, they have ended the Mackerels' 11-match unbeaten run.
On Sunday, Degerfors failed to score yet again but at least they held firm to secure a 0-0 draw with Hacken, who sit 10th and are four games without a win.
Degerfors failed to move out of the bottom two as Oster also picked up a point in a 1-1 draw at home to Brommapojkarna. An early Alibek Aliev penalty put the hosts in front before Adam Jakobsen levelled matters within seconds of the second half getting underway, keeping BP ninth in the league.