The visitors left their hosts looking distinctly second-best.
The two sides started the evening level on points, but it looked as though the hosts would be the victors as they took an early lead.
American international Carlos Bocanegra did the honors, firing home a left-flank cross from the impressive Dimitri Payet after 13 minutes.
Lyon came storming back shortly afterward though, and former Sainte man Bafetimbi Gomis showed the kind of ability that led to his transfer up-river in the first place with the equalizing goal. The French international showed great poise to bury an 18-yarder after home goalkeeper Jeremie Janot cleared a corner in his direction..
Just before half time the visitors had the lead, Mustapha Bayal putting through his own net after yet another well-taken corner from Yoann Gourcuff.
Michel Bastos got in on the act twenty minutes from time for Lyon's third goal of the evening with a simple finish after the hapless Bayal failed to deal with a long clearance from Hugo Lloris.
Finally substitute Jimmy Briand made the most of his five minutes on the pitch with the icing on the cake, netting a fourth following some fine set-piece interplay as Saint Etienne's battered defense looked on.
With near-challengers Rennes still to play this weekend, OL thus jump to joint-third on 38 points, level with Paris Saint-Germain, with whom they share an identical record. ASSE remain on 35 points, seven behind league leaders Lille, who still have a game in hand.
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