Hammarby could only blame themselves for falling behind after half an hour in Gothenburg - careless passing in defense allowed Ibrahim Diabate to intercept and score the opening goal.
The visitors equalized early in the second half when Abdelrahman Boudah rose to head in Sebastian Tounekti's cross, only for GAIS to regain the lead in the 60th minute, when Diabate converted a penalty after a handball by Oskar Agren.
Diabate capped off a remarkable afternoon by assisting Amin Boudri in the final 10 minutes - he cut inside and calmly finished into the bottom corner.
A reckless challenge from Victor Eriksson late in the game allowed Jusef Erabi to narrow the gap in the closing minutes, making it 3-2, but it wasn't sufficient to stop Hammarby's four-match winning streak from ending, as GAIS' unbeaten run extends to eight matches.
Mjallby were clearly eager to seize the opportunity 24 hours later as they traveled to face Sirius, quickly establishing a solid lead.
Seven minutes into the match, Elliot Stroud was afforded too much space in the box, and despite the angle being against him, he managed to squeeze the ball past goalkeeper Ismael Diawara.
Nine minutes later, Stroud turned into a playmaker after his first shot was saved, he squared the rebound to Jacob Bergstrom, who slotted the ball past an out-of-position Diawara.
The score remained 2-0 until 10 minutes from the end, when a free-kick was played back across the goal to Jakob Voelkerling, who bundled it in from close range.
However, Sirius were unable to mount a comeback and suffered a second consecutive loss, allowing Mjallby to go four points clear at the top, with their current unbeaten streak matching that of GAIS - eight matches.
AIK has reclaimed third place from Elfsborg and closed the gap to Hammarby to just one point thanks to a 3-0 victory over struggling Degerfors, who have now lost six matches in a row.
Andronikos Kakoullis ended a two-month goal drought by scoring twice, once before half-time and once after, before Bersant Celina added a third in injury time.
The biggest surprise of the round occurred in Varnamo, where the home team finally secured their first win of the season at the 15th attempt, defeating Djurgarden 1-0.
To add to the excitement, the goal came in the 94th minute of the match - Mohammad Alsalkhadi executed a lovely one-two inside the box with Marcus Antonsson before guiding the ball into the bottom corner, inflicting a defeat on the same team that scored five against Degerfors last week.
Both Hacken and Brommapojkarna took advantage of Djurgarden's slip by climbing above them in the standings to eighth and ninth, respectively.
Hacken achieved this with a convincing 4-1 triumph over Halmstad. Adrian Svanback, Sanders Ngabo and an Amor Layouni penalty put the hosts 3-0 ahead before halftime, then Isak Brusberg added a fourth just three minutes after the restart to secure back-to-back victories.
Malte Persson scored a consolation goal in the 93rd minute for Halmstad, who sit 11th after suffering a fifth defeat in seven.
Brommapojkarna have achieved three consecutive victories for the first time this season, as they defeated Oster at home, 2-0.Adam Jakobsen and Victor Lind scored in the second half to condemn Oster to consecutive defeats and another week in the bottom two.