In Brest, Mbappe returned from a one-match ban and fired PSG ahead on nine minutes, running from just inside the halfway line and drilling a left-footed shot into the top corner from the edge of the area.
Julian Draxler set up Pablo Sarabia for a second goal before half-time, the Spaniard sweeping home for the second game in a row having hit the winner against Bordeaux in midweek.
Angel Di Maria came off the bench for his first appearance in a month following a thigh injury, a timely boost alongside the return of Marco Verratti ahead of next week's second leg against Barcelona in the Champions League last 16. Verratti created PSG's third, somewhat inadvertently, as he prodded across goal and straight into the chest of Mbappe, wrong-footing Brest goalkeeper Sebastien Cibois.