Lynel Kitambala scored in injury time at the end of extra time to see Auxerre past Ligue 2 rivals Dijon and into the last 16 of the Coupe de France.
With the game locked at 2-2 after 90 minutes, the teams went to extra time and appeared set for a penalty shoot-out until the striker's late intervention.
Auxerre had led 2-0, Jamel Ait Ben Idir scoring in the first half and Paul Ntep adding a second in the 64th minute.
Fabrice Berenguer quickly responded and Julio Tavares forced an extra period, but Kitambala had the final say.
Cannes, who beat top-flight Saint Etienne to reach this point, got through again with a 1-0 win over fourth-tier rivals Plabennec. Belkacem Zobiri scored the only goal in the 28th minute.