Pedro Gallese made two saves for the Lions for his 11th career MLS shutout.
Montreal (0-1-0, zero points) played with 10 players after Romell Quioto was given a red card for violent conduct in the 66th minute. Quioto shoved Orlando City's Antonio Carlos and Robin Jansson to earn the ejection.
But Orlando City also went down to 10 players in the 81st minute when Jansson was ejected for drawing his second yellow card of the match. He drew his first during the incident with Quioto.
Sebastian Breza made one save for Montreal.
Both teams took eight shots. Orlando City put three on goal and Montreal had two.
Pato scored in the 49th minute to break the scoreless tie. It was the first MLS goal for the former Chelsea and AC Milan man, who joined Orlando last season but missed of the 2021 campaign with injuries.
Ruan had the ball on the right and sent a dribbling pass to his left in front of the net. Breza got a hand on it but not enough to keep it from reaching Pato, whose right-footed shot hit off defender Gabriele Corbo en route to finding the net.
Orlando City tacked on another goal in the 59th minute after Montreal was unable to clear the ball out of its own end. The ball soon made its way to Pereyra and he fed Michel, who booted a right-footed shot past Breza.
Montreal had a chance in the 90th minute but Joaquin Torres sent the left-footed direct kick well over the net.
Orlando City had two solid chances in the first half. Pereyra sent a right-footed shot over the net in the 29th minute and Pato missed on a header in the 41st minute.
Montreal's best chance in the half was in the 35th minute when Djordje Mihailovic's straightaway right-footer was saved by Gallese.