When the two teams came in at half-time goalless, no one could have predicted the chaos that followed. It all started four minutes after the break, when Simon Strand sent a crisp volley sailing past Kristoffer Nordfeldt and into the bottom corner.
AIK needed only eight minutes to level, as Abdihakin Ali ran onto a neat through ball and finished well, but from then on the visitors dominated, retaking the lead before the hour-mark as Kamilcan Sever tapped home after Nordfeldt had done just enough to deny Anton Kurochkin, and it was 3-1 soon after when Wilmer Odefalk cut inside from the left wing and rolled the ball home.
BP's fourth was a calamity for the home defence, as neither of the two players that went for the same ball inside the six yard box dealt with it, allowing Sever a second tap-in, and 20 minutes from time it was 5-1 - Sever burst into the area but rather than go for the hat-trick, he squared for Kurochkin who set himself before finishing in style, as a chorus of boos rang out from the home fans.
However, AIK then began the most remarkable comeback, beginning with Taha Ayari running onto a low ball into the box and firing in, then the hosts brought on Sixten Gustafsson, which turned out to be a stroke of genius, as he bundled the ball over the line following a free-kick, and then made it 5-4 with six minutes to play by heading home a Lucas Assadi cross.
Time looked to have run out for AIK, but deep into added time Ali picked out Johan Hove on the left side of the box, and he shaped to shoot around the goalkeeper only to tuck the ball home at the near post to complete the comeback.
However, there was to be one more twist - the Bromma Boys immediately broke down the left side and Oliver Zanden squared the ball across goal for the awaiting Mads Hansen, who applied the first-time finish from the centre of the box to win Brommapojkarna three memorable points in dramatic fashion.
The win ends BP's two-game losing streak but after all that, they stay in 11th place. AIK are winless in five and have lost three of their last four - they sit ninth.
There was just the one goal at Gamla Ullevi but that was plenty for league leaders Sirius to get the better of GAIS and go 11 points clear for the time being, while it's two losses in the last three for the Mackerels.
Isak Bjerkebo was the difference-maker, scoring his 14th of the season but his first since mid-August, receiving a Joakim Persson ball across goal and firing home from six yards to complete a wonderful attack from the visitors in the 78th minute.
GAIS didn't produce enough to get back into the match, and they remain 10th with just one win in four, while Sirius have made it four wins in a row since their run of three straight defeats.
Second-half goals remained en vogue in Hallevik, where Mjallby came from a goal down to draw with Degerfors, who climb out of the bottom three, while the home side extend the margin between themselves and the relegation zone to four points.
Six minutes after the break, the visitors worked a free-kick into the Mjallby box where Sebastian Ohlsson's ball across fell kindly for Arman Taranis to turn home from 10 yards out. But the hosts were level just four minutes later, as Degerfors failed to clear their lines properly, and when the ball dropped to Jeppe Kjaer at the edge of the box, he struck low through the crowd and nestled the ball in the bottom corner.
Mjallby remain without a win in seven in Allsvenskan and 11 in all competitions, including a humiliating 1-0 loss to third-tier Trollhatten in Svenska Cupen in midweek to end their title defence at the first hurdle. Degerfors have picked up a first point in three matches.
Follow the Allsvenskan run-in on Flashscore.