The Impact had to rely on a stoppage time penalty kick by Patrice Bernier to dispatch a plucky FC Edmonton side from contention for the Voyageurs Cup.
Jack McInerney and Frank Jonke both scored twice for their respective sides, while Jeb Brovsky and Patrice Bernier each had a second half goal for Montreal.
The Impact pressed from the opening whistle, and they enjoyed the lion's share of possession as Edmonton was content to sit back and defend. This strategy turned out to be the wrong one for the visiting side, as Montreal struck twice within the first 20 minutes.
At the 10-minute mark, Justin Mapp got the ball and made a driving run down the right side before sliding a pass over to McInerney, who one-timed a shot that found the back of the net.
McInerney doubled his tally just seven minutes later after Sanna Nyassi started a counter attack down the left flank and initiated an attack that eventually found the former Philadelphia Union striker inside Edmonton's penalty area. The 21-year-old side-footed home, and Montreal took control of both the game and the series with a 2-0 lead at Stade Saputo.
In the 34th minute, McInerney thought he had a third goal, but his headed effort was judged to be offside after he broke past the Eddies' defensive line in pursuit of a floated Mapp free kick.
Montreal kept the pressure going to start the second half, and Brovsky put the Impact up 3-0 with a header off a corner in the 47th minute. At that point, the hosts seemed to take their foot off the gas and Edmonton clawed its way back into the game.
The NASL side found ample time and space to build its attack, and it was rewarded in the 67th minute when Jonke notched the first of two goals within a three minute span. Influential teenager Hanson Boakai slipped the big striker a short throughball that was lifted over the onrushing Impact 'keeper to give Edmonton life.
Jonke then converted a penalty kick in the 70th minute after Montreal defender Karl Ouimette fouled a player inside the 18-yard box, giving the Eddies a tie on aggregate and a potential win based on the away goals rule.
However, despite defending for their lives over the final 20 minutes plus stoppage, the Eddies would ultimately fall after to a controversial call by the referee. After a seemingly legitimate penalty kick for Montreal was instead given as a free kick on the edge of the Edmonton area in the 88th minute, the Impact would get their spotkick five minutes into added time.
Edmonton defender Mallan Roberts was judged to have handled the ball inside the area, and Impact captain Bernier stepped up and coolly slotted home. The goal sent the home side into raptures while leaving several Edmonton players strewn about the pitch.
With the win, Montreal advances to the Canadian Championship final, where it will face the winner of Wednesday night's semifinal second leg match between Vancouver and Toronto.