Substitute Robert Beric denied second-placed Marseille when his equalizer earned bitter rival Saint-Etienne a 2-2 draw on Friday.
In snow and freezing temperatures, the Slovenian striker bagged his second French league goal of the season in the 75th minute when he connected with a cross from the right, four minutes after coming on to the field.
Marseille is unbeaten in 10 matches in all competitions but could be overtaken by third-placed Monaco when the defending champion visits Angers on Saturday.
Ten points clear at the top, Paris Saint-Germain travels to Toulouse on Saturday ahead of its midweek trip to Real Madrid for a Champions League last-16 first leg.
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Marseille may be enjoying its best season for years but the team is struggling at the Geoffroy Guichard stadium, where it has won eight times in 53 games.
Florian Thauvin opened the scoring for Marseille in the fourth minute when he volleyed past Stephane Ruffier, his sixth goal of 2018.
Kevin Monnet-Paquet leveled five minutes later before Morgan Sanson made it 2-1 to the visitors in the 20th with a fine volley from Bouna Sarr's precise cross.
Beric, who replaced Monnet-Paquet, then pounced on a center by Jonathan Bamba to salvage a point for the hosts.
Saint-Etienne, which has won 10 league titles, one more than Marseille, is 12th in the standings.