New St Etienne manager Claude Puel got off to a winning start as Robert Beric's late header secured a dramatic 1-0 win over derby rivals Lyon at Stade Geoffroy-Guichard.
Puel was only appointed on Friday, taking up his first role since being sacked by English Premier League side Leicester during February.
The French coach had been handed a baptism of fire, his side sitting second-last in table as they prepared for the Rhone-Alpes showdown.
Lyon, meanwhile, were looking to build on a 2-0 Champions League win at RB Leipzig, and out to secure a first Ligue 1 success since mid-August.
The visitors went close inside the opening two minutes when a clearance from St Etienne defender Thimothee Kolodzieczak hit Martin Terrier and flew over the crossbar.
With tempers starting to rise, Lyon defender Marcal was shown a yellow card in the 16th minute for a late tackle on St Etienne forward Charles Abi.
The hosts almost broke the deadlock when Ryad Boudebouz's shot was pushed onto the post by Lyon goalkeeper Anthony Lopes.
At the other end, Memphis Depay sent a long-range free-kick just wide as the first-half finished goalless.
Lyon thought they had broken the deadlock on the hour.
Houssem Aouar raced onto a pass down the left and into the penalty area, before clipping a low, angled shot into the far corner.
The midfielder's celebrations, though, were cut short by an offside flag, which looked a very marginal call from the referee's assistant.
Lopes had to remain alert as the Lyon keeper produced another good reaction save to deny Denis Bouanga.
Aouar continued to provide Lyon with an outlet, and weaved his way into space before seeing a goalbound shot pushed behind for a corner.
Lyon substitute Moussa Dembele thought he had found a way through when he met a cross with a downward header, but again St Etienne goalkeeper Jessy Moulin produced a fine save.
Defender Leo Dubois hobbled off for the closing stages, leaving the visitors with only 10 men having used all of their substitutes, before Aouar shot wide.
Just when it looked like both sides would have to settle for a point, Beric headed home a winner in the final minute.
Boudebouz found space on the far touchline before floating a deep cross into the Lyon penalty area, where Beric planted a diving header into the top corner to spark wild celebrations from the home fans.
