Nancy were condemned to relegation from Ligue 1 following defeat to Bastia at Stade Marcel Picot.
Anthony Modeste's 72nd-minute strike sent the Lorraine club down and ensured Bastia retained their own top-flight status.
Bastia led through Ilan on 47 minutes and, while Sebastien Puygrenier levelled on the hour, Modeste decided Nancy's fate before next weekend's final round.
Nancy had revived their hopes of staying up after picking up 17 points in eight games during February and March, but a 20-game winless run at the start of the season proved too much to overcome.
Patrick Gabriel's side were the more likely scorers in a scoreless opening half, though.
Bastia's veteran goalkeeper Mickael Landreau did well to block Benjamin Moukandjo's low shot after he had latched on to Thomas Mangani's clever flick.
Landreau then relied on his reflexes to keep out a Mangani free-kick as it took a deflection on its way through to him.
Puygrenier headed over just before half-time after Julien Sable failed to clear a Mangani corner.
Nancy goalkeeper Damien Gregorini made his first real save a minute after half-time when he got down to keep out Ilan, but the Brazilian won out moments later.
Modeste flicked on Sable's delivery at the edge of the area and Ilan beat Gregorini to the ball to head in the opener.
Nancy were not willing to go down without a fight and deservedly drew level when Puygrenier was left unmarked from a Mangani corner to slot home with his left foot.
But the home crowd was left hushed 18 minutes from the end as Modeste struck.
Claudio Beauvue rolled the ball across the top of the area for Modeste, who perfectly picked his spot with a shot that beat a diving Gregorini and went in off a post.