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.
Elsewhere, Rennes climbed to 14th with a convincing 3-0 home win over Bastia.
Romain Alessandrini and Ola Toivonen put the home side in control inside half an hour, before Jean Makoun added a third just before the hour mark.
It was a crucial win for Rennes as they moved eight points clear of the drop zone, while for Bastia it was a third defeat in four.
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