Toronto dropped to 11-14-8, giving Columbus an Eastern Conference playoff spot.
Warren Creavalle opened the scoring for Toronto in the 20th minute.
Montreal's Heath Pearce was sent off in the 82nd minute for a scissors tackle on substitute Dominic Oduro. Toronto's Jonathan Osorio was ejected in stoppage time for a tackle on Felipe.
The Impact's Hassoun Camara soon followed for a second yellow.
Toronto star Michael Bradley sat out because of yellow card accumulation.
Montreal is 6-18-9.
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