Orlando City (6-8-1) has lost a franchise-record seven consecutive games and has conceded 19 goals during that span.
Montreal (5-11-0) has won two in a row - both against Orlando City, which the Impact beat 3-0 on June 13 - and three of its last four.
The Impact took the lead on Orlando City's own goal in the 13th minute. Defender Lamine Sane's header redirected a cross by Montreal's Matteo Mancuso past goalkeeper to open the scoring. Piatti made it 2-0 in the 84th when, at the top-left corner of the 6-yard box, he took a feed from Alejandro Silva and evaded sliding goalkeeper Joe Bendik before finishing into an empty net from point-blank range. Montreal was flagged offside on the field, but was awarded the goal after replay review.
Evan Bush had one save in his second consecutive shutout for the Impact.
Kickoff was delay nearly 30 minutes due to inclement weather.
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