Les Verts opened the scoring through Brandao’s 55th-minute header, with winger Franck Tabanou sealing the win with a close-range volley five minutes later.
Lille subsequently went down to 10 men after Florent Balmont was dismissed for protesting the second goal.
The result means St Etienne are now just three points behind Lille, who are in Ligue 1’s third and final Champions League spot.
Leaders Paris Saint-Germain and fellow big spenders Monaco occupy the top two places.
- Sports & Recreation
- Florent Balmont
- Franck Tabanou