Owen Lynch snuck a single past the second baseman to score Cody McCormack with the winning run as P.E.I. rallied with two runs with two outs in the bottom of the seventh.
Quebec had scored four runs in the top of the inning to take the lead.
Colby Huggan recorded the victory, pitching in relief of starter Jack Sherrington.
Lynch, Sherrington and McCormack all recorded a pair of hits. Kal White was P.E.I.'s player of the game, with a key two-run triple in fifth inning to tie the game.
P.E.I., which defeated Ontario 11-4 and lost a tough eight-inning game 9-8 to B.C. on Thursday, plays Saskatchewan today at noon Atlantic.