Two goals inside the last 20 minutes gave Brest their second Ligue 1 victory of the season and increased Nancy's misery at the Stade Marcel Picot.
Late breakthroughs from Thomas Micola and Larsen Toure mean the home side have lost all three games on their artificial surface this season.
Brest started brightly and created the game's first chance after two minutes when Nolan Roux's shot needed goalkeeper Gennaro Bracigliano to save. The visitors threatened again in the 18th minute. Toure combined with midfielder Mario Licka in front of goal but again came off second best with a shot at Bracigliano.
The home side had to wait until the 31st minute for their first opening, Bakaye Traore volleying just over the bar following good approach play from Michael Chretien and Julien Feret. And eight minutes later Nancy again went close when Landry N'Guemo fired over.
Nancy pressed at the start of the second half and Brest goalkeeper Steve Elana needed to be at his best to deny Alexandre Cuvillier in the 54th minute. Five minutes later and Traore brushed the post with a shot which followed a defensive error from Bruno Grougi.
The home side were pressing for the decisive opening goal and Marama Vahirua brought a great save out of Elana in the 62nd minute. But the visitors took control of the contest by netting the opening goal against the run of play after 69 minutes.
Andre Luiz lost the ball to Micola, who gratefully took advantage by beating Bracigliano with a close-range shot. Soon after Feret almost doubled the advantage when he headed inches over following a Chretien cross.
But the points were made safe in the second minute of injury-time when Toure was released on the right by Micola and he advanced before shooting past Bracigliano.
