Mjallby had been the big winners on Thursday, as they beat fellow title-chasing Hammarby to go three points clear of AIK, whose match at Malmo finished goalless.
Malmo, who have been trying to keep pace with the top four, lost further ground on Sunday when they were beaten 1-0 by IFK Goteborg away from home.
Shortly before the hour mark, Tobias Heintz curled in a free-kick which was nodded home Kolbeinn Thordarson to give Goteborg all three points and back-to-back wins after a run of one win in six.
The champions were six points outside the European places by full-time as Elfsborg had cruised to a 4-1 win away at Halmstad - a fifth win in a row for the men from Boras.
A Simon Hedlund penalty down the middle and a deflected 20-yard strike from Frederik Ihler sent Elfsborg on their way inside the first quarter of the match, before Ibrahim Buhari diverted the ball into his own net after half an hour to give the home side hope.
However, a Rasmus Wikstrom header from a corner early in the second half but Elfsborg back in control, then Taylor Silverholt sealed the win with a neat finish after a slip from the Halmstad defence. Despite a third loss in a row, HBK continue to hover above the relegation zone.
AIK wiped out Mjallby's three-point advantage for 24 hours but stayed second on goal difference following a 1-0 win away at Brommapojkarna despite finishing with 10 men.
The Solna side's luck was in midway through the first half when Daleho Irandust saw his penalty saved by Kristoffer Nordfeldt, then they capitalised just before the break when Bersant Celina's shot was rebounded to Johan Hove, who guided in the winner.
Anton Saletros was sent off 12 minutes from time for a second yellow card, but BP could not find a way through and fell to a fourth loss in succession.
Mjallby knew it would be "as you were" with a victory away at Norrkoping on Monday, and that's how things were heading when Ludwig Thorell put them in front just before half-time with a lovely curling finish.
Despite plenty of good opportunities to wrap up the win, the Hallevik side were under pressure during the second half, and Norrkoping grabbed a deserved leveller five minutes from time when Arnor Traustason floated a 25-yard free-kick into the back of the net.
The draw means Mjallby move onto 27 points, one clear of AIK, with Elfsborg on 25 but with a game in hand on the top two.
Hammarby stay fourth, one point behind Elfsborg and five clear of Malmo after they picked up a 1-0 win at home over Degerfors on Monday evening.
It took a while for the hosts to break their opponents down, but a low strike from the edge of the area from Nahir Besara after an hour was the difference-maker in the end and earned the Bajen a much-needed first win in three, as Degerfors slip to three losses in four.
Elsewhere, a 2-1 come-from-behind win over Sirius at home has taken GAIS up to seventh, overtaking Hacken, who were pegged back in a 1-1 draw away at Djurgarden.
In the battle of the bottom two, a 90th-minute equaliser from Lukas Bergqvist denied Varnamo a first win of the season and salvaged a 1-1 draw for Oster, who stay five points clear of their hosts..