First half goals from Alassane Plea and Younes Belhanda set Nice on their way with Ivorian Jean Michael Seri .
First half goals from Alassane Plea and Younes Belhanda set Nice on their way with Ivorian Jean Michael Seri rounding off with his ninth goal of the campaign on 65 minutes.
Nice have a three-point advantage on second-placed Monaco who whipped Bastia 5-0 on Saturday with Paris Saint-Germain four points adrift of the leaders after falling 3-0 at Montpellier.
Nice captain Dante admitted the win was a psychological boost ahead of next weekend's clash with the champions at the Parc des Princes.
"We'll arrive in Paris next week with a four-point lead," said the Brazilian defender.
"There will be a little less pressure. But we mustn't get carried away. Despite the defeat at Montpellier, Paris remain a great team. We've got to be prepared to suffer in Paris."
Toulouse, the only team to have beaten both Monaco and Paris Saint-Germain this campaign, remain stuck in eighth place.
Earlier Florian Thauvin struck just after half-time at the Stade Velodrome before fellow Premier League cast-offs Bafetimbi Gomis and Clinton Njie scored late goals after Benoit Pedretti was sent off for Nancy.
It was just a fifth win in 16 matches for Marseille this season as the fallen French giants climbed back into the top half of the table, 18 points behind leaders Nice.
Rennes moved up to fourth as second-half goals from Paul-Georges Ntep and Kamil Grosicki earned them a 2-0 win at home to Saint-Etienne.
On Saturday, Radamel Falcao scored twice as Monaco thrashed Bastia 5-0, but PSG crashed to a 3-0 defeat at Montpellier to lose ground in the title race.
However, the action was overshadowed by incidents in Metz where Lyon goalkeeper Anthony Lopes was taken to hospital with hearing problems after home fans targeted the Portugal international with firecrackers.
Fortunately, the 26-year-old confirmed there would be no lasting damage, but Metz could face heavy sanctions from authorities including forfeiting a game they had led 1-0 before it was abandoned in the 31st minute.