Nice fell five points off the pace in the Ligue 1 title race on Sunday, despite fighting back to draw 2-2 with Rennes after a dismal first half at Roazhon Park.
Lucien Favre's side had responded to a 3-0 defeat against league leaders Monaco with victory over Saint-Etienne in midweek, but they soon found themselves two goals behind to Rennes - and lost top-scorer Alassane Plea to injury before half-time.
Morgan Amalfitano opened the scoring after seven minutes, lifting a fine finish over Yoan Cardinale following a one-two with Giovanni Sio, who then added a second in controversial circumstances.
The Ivory Coast international was initially flagged for offside after firing in from Sanjin Prcic's deflected effort, but, after consulting with the linesman, referee Johan Hamel awarded the goal.
Plea was withdrawn two minutes before the break, having challenged with Pedro Mendes, but Nice responded after the restart as Anastasios Donis swept a shot into the net with around half an hour remaining.
Although left-back Dalbert also picked up an injury, Valentin Eysseric completed the comeback after running through from Jean Michael Seri's measured pass.
Despite some late pressure, Nice could not complete the comeback and are now two points behind second-placed Paris Saint-Germain, with Monaco a further three in front.