© Getty Images
The hosts had a chance to take the lead inside the opening 10 minutes when Brandao tried to volley in from a corner, but it was blocked in the six-yard box.
Marseille continued to create the better of the chances and were finally able to break the deadlock 64 minutes in, with Nicolas N'Koulou nodding the ball in from close range from connecting with a Dimitri Payet free kick.
Zouma tried to create a scoring opportunity for Saint-Etienne as they searched for an equaliser, but his run down the wing was halted.
Gignac tried to put the result beyond doubt inside the final 10 minutes, beating a number of defenders before unleashing his shot, but Stephane Ruffier was able to deny the striker.
The save proved vital for the hosts as Brandao found the back of the net deep into stoppage time after Marseille forgot to mark him, giving him a free header for the equaliser.
The result leaves Saint-Etienne in fourth place in the table, just above Marseille.