Pierre-Emerick Aubameyang had a chance for the away side in the first minute, but he was unsuccessful in his finish.
Brandao was next to have an opportunity for Saint-Etienne, but his effort went wide of the mark.
Aubameyang had his second chance on 13 minutes, though he could not find the target to give his side the lead.
Geoffrey Dernis got a strike in for Brest, but his shot was way off the mark.
Brandao then gave the away side the lead on 50 minutes, applying the finish well to Yohan Mollo's pass.
Florian Raspentino found himself on goal for Brest, but struggled to get a clean shot at goal.