New Montpellier coach Rolland Courbis slipped to defeat in his first game in charge on Friday as Saint-Etienne earned a 1-0 win.
Courbis returned for a second stint in charge of the 2011-12 Ligue 1 champions earlier this week following the resignation of Jean Fernandez.
But the 60-year-old could not inspire the struggling hosts to victory, Montpellier succumbing to a defeat that extends their winless run to nine games.
Saint-Etienne dictated for much of the first half, with winger Franck Tabanou going close to giving them the lead on multiple occasions.
Christophe Galtier s men finally broke down the home defence in the 75th minute when former Leeds United forward Max Gradel turned home Faouzi Ghoulam s low cross at the far post.
Montpellier failed to mount a response, allowing Saint-Etienne to hold on and claim their third league win in four games.
