Mjallby would have hoped their convincing win on their UEFA Champions League debut over Lincoln Red Imps in midweek would have been the catalyst for an upturn in league form, but instead, the champions fell to their fifth Allsvenskan defeat of the season.
That didn't look to be the case when they took the lead in just the third minute, when Villiam Granth played a square ball to Elliot Stroud, who showed why he is attracting attention from around Europe by thundering a low, 25-yard effort into the bottom corner.
The lead lasted less than 15 minutes, as a corner routine resulted in Melker Hallberg sending a teasing cross to the back post, which Aboubacar Keita leapt to meet and powered in with his head.
1-1 was how things stayed until just over 20 minutes remaining, when a cross from the Kalmar right was not properly cleared, instead flicked straight to an unmarked Charles Sagoe Jr on the left side of the box, and he had time to take it down and fire low past the scrambling away defence.
Kalmar retain their impressive unbeaten run at home to move level on 17 points with the champions, who sit 11th and 10th, respectively.
Djurgarden are up to third in the table thanks to a narrow win at Degerfors, their third win in a four-game unbeaten run, while the hosts have now lost four on the spin.
The only goal of the game came late in the first half, when Hampus Finndell's shot from the edge of the area was blocked and bobbled on through to Bo Hegland, who lifted the ball over goalkeeper Matvei Igonen from close range.
Igonen's smart stops in the second half kept the score down, but Djurgarden had done enough to come through the test to move into the European places on goal difference. Degerfors remain in the relegation play-off place, three points shy of Goteborg.