Bernier broke a scoreless tie in the 34th minute on a penalty shot after Montreal's Andres Romero went down in the box following a collision with Toronto's Ashtone Morgan.
Di Vaio doubled the advantage for the Impact (3-0-0) in first-half stoppage time when he collected a through-ball from Davy Arnaud and scored on goalkeeper Joe Bendik.
Toronto (1-2-0) got a penalty-kick goal in the 68th minute from Robert Earnshaw.
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