Max Gradel's early strike for Les Verts was cancelled out by Mathieu Duhamel before half time, but the Savoy Crosses could not avoid the drop after Gradel scored a second from the penalty spot late on.
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The win also means that St-Etienne are still in the hunt for a place in next season's Champions League along with Marseille and Monaco.
Evian made an energetic start in their bid to stay up as Duhamel and Adrien Thomasson were denied with early efforts.
However, they fell behind when Gradel's strike from the edge of the area found the top corner of Benjamin Leroy's net.
Dutch striker Ricky van Wolfswinkel then squandered two chances to double Les Verts' lead before Evian managed to get back on level terms.
Their equaliser came when a fast counter-attack finished with Thomasson picking out Duhamel, and the forward duly netted from close range.
Duhamel could have given Evian the lead midway through the second half when he headed wide, but instead St-Etienne were given the chance to restore their advantage with eight minutes left as Cedric Cambon bundled over Gradel in the penalty area.
Gradel calmly dusted himself down to send the spot kick into the top corner of Leroy's net.
Evian's misery was compounded in stoppage time when Kassim Abdallah was sent off as they were condemned to relegation.body check tags ::