The visitors were awarded a penalty after Lilian Brassier fouled Randal Kolo Muani. While Mbappe’s spot kick effort was saved, he netted the rebound a minute before stoppage time.
PSG are second with 21 points, a point behind leaders Nice. Brest are sixth with 15 points.
Warren Zaire-Emery, 17, displayed his skills 16 minutes into the match when he fired a thunderous shot into the upper left corner to hand PSG a 1-0 lead.
Mbappe doubled the score with his 250th club goal when he calmly slotted the ball into the bottom-left corner in the 28th minute.
Steve Mounie was roared on by the home fans when he netted a close-range shortly before the interval and Jeremy Le Douaron levelled the score just after the restart.
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