Mjallby had ambitions of going to Strawberry Arena and leaving as the league leaders, and they gave themselves every chance when taking the lead 10 minutes in.
Axel Noren played a ball over the top, spotting the run of Elliot Stroud, who met the ball with his head and guided it in off the post for his first of the season.
But the advantage lasted only 13 minutes - Mjallby failed to clear a corner which fell to Victor Andersson on the left side of the area. He opened up his body and curled a beautiful right-foot shot through the crowd and into the opposite corner.
Both sides had chances either side of the break, and the winner arrived just past the hour mark, when a Dino Besirovic effort from outside the box was deflected. With all the pace taken out of the strike, it allowed Anton Saletros to pounce and poke it beyond the advancing Noel Tornqvist.
In added time, AIK were awarded a penalty for a foul on John Guidetti, which seemed to have taken place outside the penalty area. Justice perhaps prevailed when Tornqvist saved Guidetti's spot-kick, but AIK had done enough to return to winning ways and retake first place.
For Mjallby, meanwhile, the 2-1 loss saw their five-match winning run come to an end.
AIK have clear daylight between themselves and the chasing pack after Hammarby were held 1-1 at home to Norrkoping, leaving them with just two wins in their last five.
The visitors deservedly took the lead 15 minutes in, when an attempted through ball ricocheted into the path of the oncoming Isak Sigurgeirsson, who took on a first-time strike from over 20 yards which he curled into the top corner.
In the 33rd minute, Hammarby equalised in very similar fashion - a pass to the edge of the area deflected back to Montader Madjed, who picked out the top corner in style.
The second half was full of chances, top class goalkeeping and both sides hitting the woodwork, but somehow it stayed 1-1 to leave the Bajen on 17 points, while Norrkoping are seventh on 10 points.
On Monday night, Djurgarden put their UEFA Conference League disappointment behind them to beat Goteborg 2-1 away from home, taking them to four league matches unbeaten and up to sixth.
The Iron Stoves made a quick start and were ahead four minutes in when Santeri Haarala's ball from the right found Tokmac Nguen, who teed himself up and slammed a volley home from six yards.
The home side then came alive, and were rewarded for creating numerous chances when Seedy Jagne's ball across the box after 25 minutes was turned into his own net by Marcus Danielsson.
IFK could not find the go-ahead goal, and were punished with 13 minutes to play - Tobias Gulliksen fired over a cross, which goalkeeper Elis Bishesari could only bat down to Haarala, who applied the finish.
The loss keeps Goteborg in 11th, but as one of six teams from seventh to 12th all on 10 points.
Malmo brushed off their home defeat last time out by cruising past Degerfors 4-1 away from home. Lasser berg Johnsen and Emmanuel Ekong struck in the first half, before Hugo Bolin added a third soon after half time.
Marcus Rafferty's spot-kick reduced the deficity, only for any hopes of a late comeback to be ruled out by Anders Christiansen in added time. The champions stay fifth on 14 points, while Degerfors are among the 10-point cluster.
MFF failed to move up the standings thanks to Elfsborg also recording a win away at a newly-promoted side, as Sebastian Holmen's strike early in the second half was enough for a 1-0 victory over Oster.
That moves Di Gule within one point of Hammarby and Mjallby, while Oster have now lost six in a row without scoring.
There was joy for Varnamo who finally picked up their first point of the season at the eighth attempt, drawing 1-1 away at GAIS, though they remain bottom, two points shy of Oster.
It looked to be more of the same for the visitors when Oskar Agren's flicked header gave the Gothenburg side the early lead, only for a second goal in as many games for Johnbosco Kalu to nestle in the bottom corner after 65 minutes.
The result was disappointing for GAIS, who drop into the bottom three having failed to win any of their last five.
Overtaking the Mackerels are Sirius, who won for the second time all season with a 2-0 home success against Hacken, who sit 10th on 10 points.
Robbie Ure broke the deadlock midway through the first half, but the home side had to wait until beyond the 80-minute mark to seal the win - Leo Walta's second strike in as many games cemented a first win since the opening day.
Finally, a Yannick Agnero strike two minutes after the restart was enough for Halmstad to secure back-to-back wins for the first time this season. The 1-0 loss for Brommapojkarna ended their four-match unbeaten run.