Valentin Eysseric's first goal of the season dealt a severe blow to Lyon's title hopes as 10-man Nice snatched a late 2-1 win at Stade de Gerland.
Nice took a surprise 23rd-minute lead through Carlos Eduardo but when Lyon drew level in the 56th minute through a Maxime Gonalons penalty after Lloyd Palun was sent off, a fifth successive defeat looked on the cards for the visitors.
However, Nice not only held their high-flying hosts at bay, they even managed to snatch an 86th-minute winner themselves when Eysseric slotted home from the spot
Despite going into the game as underdogs, it was Nice who started the brighter of the two sides.
Carlos Eduardo went close early on after he was played in by Palun, but Anthony Lopes made an excellent stop in the Lyon goal to keep the scores level.
Alassane Plea also forced a good save from the keeper, but Lyon, who would have returned to top spot with a victory, had the best chance as Mouhamadou Dabo cut in from the right and unleashed a powerful right-foot shot which appeared to be heading for the top corner until Simon Pouplin got a hand to it.
Eysseric played a role in the first goal when his corner was cleared to Eduardo who produced a stunning overhead kick to give the visitors the lead after 22 minutes.
Nabil Fekir, who was called up to the France squad for the first time this week, caused problems for the Nice defence throughout and eventually won a penalty for his side as he was brought down by Palun after Pouplin had parried a shot into his path.
With the full-back already on a yellow card, there was no choice but to give him his marching orders and Gonalons made no mistake from the spot, firing the ball into the bottom-right corner.
Lyon pressed for a winner, but Christophe Jallet was wasteful with his effort as the home team were frustrated by the 10 men.
With the game seemingly heading for a draw, Bakary Kone brought down Plea in the 87th minute to give Eysseric the chance to take a big three points, which he did, sending Lopes the wrong way.