Mwalala claims the Tanzanian custodian wasted a lot of time especially in the final quarter of the game after Lawrence Juma had scored for the KPL champions.
"The match was played, I think for only 70 minutes, and then the goalkeeper [Mapigano] started wasting time especially after they scored," Mwalala told reporters after the match.
"I am not saying this is the biggest reason why Bandari lost but the goalkeeper's antics contributed a lot."
The former Nzoia Sugar coach hailed his players for playing according to their pre-match plan.
"My players did what I wanted of them and I think we deserved a win given we were the better team overall," he said.
Gor Mahia ended up winning the league's curtain-raising trophy despite Tobias Otieno being sent off after a rough challenge on Bandari's William Wadri.
The focus for the two sides now shifts to continental assignments where Gor Mahia will host Aigle Noir of Burundi in the Caf Champions League for the second leg of the preliminary round with Bandari travelling to Sudan to play Al Ahly Shendi in the Confederation Cup return match.
Both matches will be played on August 23.