Sochaux needed extra-time to see off Montceau-les-Mines to reach the final of the Coupe de France.
The minnows stood firm for 90 minutes, but were undone by two goals in extra-time.
Sebastien Grax pounced on a defensive lapse to fire Sochaux ahead on 94 minutes.
The fourth division outfit failed to fashion a response and Jerome Leroy put the tie beyond them with a goal on 112 minutes.
The second semi-final between Marseille and Nantes takes place on Wednesday.