Jack McInerney scored Montreal's (6-19-10) lone goal. Goalkeeper Evan Bush made one save.
Ryan Meara made two saves for the Red Bulls (12-10-12), who received a goal from defender Connor Lade in the 84th minute.
The Impact finished group play with a 3-0-1 record.
Montreal entered the match having defeated New York 1-0 in CONCACAF play on Sept. 17. The teams had played twice during the MLS regular season, tying 2-2 on April 5, and New York winning 4-2 on Aug. 28.
The match was important for the Impact, who needed a win to move from sixth to a top four CONCACAF playoff seeding. A top-four seed would allow the Impact to host the second half of a home-and-home playoff series at Olympic Stadium in February 2015.
While Montreal was attempting to solidify its position in the CONCACAF tournament, New York was attempting to round its game into form for the upcoming MLS playoffs. The Red Bulls are battling for post-season positioning.
The match was contested in a driving rainstorm. Benefiting the sub-par conditions, neither the Impact nor the Red Bulls generated much in the way of scoring chances in the opening 45 minutes.
McInerney nearly gave Montreal a 1-0 lead in the 35th minute, but his shot from the box sailed over the New York goal. Five minutes later, Bush snuffed out New York's best scoring opportunity of the first half as he dove onto Lloyd Sam's pass with Eric Stevenson bearing down.
The second half started in much the same fashion as the first, when Calum Mallace's header in the 64th minute was wide of the net.
McInerney's goal in the 70th minute opened the scoring. McInerney tapped Andres Romero's goalmouth feed past Meara. Montreal appeared to push the advantage to 2-0 five minutes later, but the goal was disallowed.
Which came back to haunt the Impact when Lade equalized in the 84th minute.