New manager Landry Chauvin watched his Brest team miss out on a draw on the opening day of the Ligue 1 season when they conceded a stoppage-time winner to Nancy midfielder Yohan Mollo.
The home side had dominated the match from the fifth minute when Mollo's free-kick found Sebastien Puygrenier and his header went inches over the bar.
Lossemy Karaboue carved out another chance for Nancy in the 32nd minute when he freed Thomas Mangani but his left-foot shot from 25 yards was just wide.
Two minutes later Brest had their best chance of the match when Bernard Mendy crossed towards Charlison Benschop in front of goal but his left-foot volley - the visitors' only shot on target - was blocked by goalkeeper Guy Roland Ndy Assembe.
It was a similar story in the second half, with Brest hanging on despite Nancy creating a host of chances.
Goalkeeper Alexis Thebaux went full stretch to stop a good shot from Mollo three minutes into the second half and went down to his left to keep out another strike from the dangerous Mollo.
When the Brest defence failed to clear a corner on 52 minutes, the ball fell to Mangani at the edge of the box but his superb volley was again stopped by Thebaux.
The Brest goal continued to live a charmed life when on 70 minutes Benjamin Moukandjo crossed from the left towards Karaboue racing into the middle and his powerful left-foot shot skimmed the outside of the post with Thebaux beaten.
The breakthrough came in the third minute of stoppage time when Mollo took a quick free-kick on the left just outside the box and finally beat Thebaux for the winner.