Frederic Sammaritano's strike was enough for 10-man Auxerre to upset the odds and defeat holders Guingamp 1-0 to reach the Coupe de France final.
Ligue 1 side Guingamp were favourites to defeat the second-tier side in Tuesday's contest at Stade de l'Abbe Deschamps and book a return to the Stade de France.
