With leaders Paris Saint-Germain and Monaco looking set to claim the top two spots in France's top flight, the scramble goes on for third and a place in the qualifying rounds of next year's competition.
Both sides were in action on Sunday, Salomon Kalou's dramatic stoppage-time winner earning Lille a 1-0 success at home to Guingamp to heap pressure on Saint-Etienne.
Christophe Galtier's side responded strongly, however, inflicting a second straight home league defeat on Lyon.
Saint-Etienne went ahead through Mevlut Erding's 28th-minute opener, but were pegged back six minutes before half-time by Alexandre Lacazette's strike.
The visitors clinched all three points through Max Gradel 16 minutes from time to open up a six-point gap over Lyon, who harbour hopes of reaching next year's UEFA Europa League.
