Ibrahima Wadji’s 117th-minute close-range strike was the decisive goal for Saint-Etienne, who had a man advantage for much of the game after Papa Diallo’s early red card.
Two years after a shambolic relegation Saint-Etienne came third in Ligue 2 this season, while Metz were third from bottom in Ligue 1.
For northern outfit Metz this was a record seventh relegation from the top flight since the turn of the century.
© Agence France-Presse
Photo: Twitter @ASSEofficiel