Montreal ended a two-game losing streak, recording its first win against Atlanta since April 15, 2017. Atlanta United has lost two of its past three after a three-game winning streak.
The Five Stripes broke the stalemate early in the second half when Jake Mulraney, just off the bench, fired from the top of the box in the 48th minute to give the visitors a 1-0 lead.
Montreal quickly responded, Quioto tucking it into the top far corner in the 50th minute. He struck again to give Montreal a 2-1 lead in the 55th minute, converting a penalty conceded by Anton Walkes.
Atlanta held the advantage in possession in the first half but struggled to get shots on target, with only two of their six attempts getting through.
Montreal goalkeeper James Pantemis nearly served the opening tally to United early on. In the second minute, his clearance rolled straight to Josef Martinez, who couldn't get a shot off, the ball rolling to Santiago Sosa, whose attempt hit the outside of the net.
Quioto had a chance for the home side in the 15th minute, taking a feed from Mathieu Choiniere and speeding up the pitch after an Atlanta turnover in the other end. But the Honduras international couldn't get a shot off as he battled with defender Miles Robinson in the area.
Nine minutes later, Quioto's header off a cross from midfielder Djordje Mihailovic missed the right side of the net by inches.
Atlanta had several chances to close out the half. In the 38th minute, Pantemis jumped to direct an Ezequiel Barco shot over the bar and in the 45th minute, the Argentina youth international dribbled through Montreal's defense and drew Pantemis out, but his shot hit the crossbar.
In the third minute of first-half stoppage time, Sosa's long-range shot was denied by a diving Pantemis.