Gaetan Laborde scored one goal and played a key role in another as Nice defeated Marseille 3-1 in Ligue 1 on Sunday to leave Paris Saint-Germain eight points clear at the top.
Marseille had been the form team in France since the World Cup, but a first loss in 10 league games dealt a heavy blow to their hopes of catching bitter rivals PSG.
Sofiane Diop headed Nice ahead at the Velodrome and Laborde doubled the advantage before half-time. Ruslan Malinovskyi's goal gave Marseille hope, but Billal Brahimi secured a fourth win in five outings for Nice under interim coach Didier Digard.
"They (Nice) are going through a good patch," said Marseille coach Igor Tudor, whose side host PSG in the last 16 of the French Cup on Wednesday.
"We have to forget about this match and think about what's next. We need to turn the page and refocus. You can't win every match."
Khephren Thuram wasted an early chance for Nice when he steered wide from the edge of the box, with Kasper Schmeichel saving well from Marseille's Jonathan Clauss and Cengiz Under.
Nice grabbed the lead on 38 minutes when Laborde's fierce swerving drive was parried by Pau Lopez and Diop dived to head in the rebound.
The visitors soon struck again as Lopez clawed out a low curling effort from Thuram and Laborde reacted quickest to slam the ball in at the near post.
Terem Moffi, whistled with every touch by Marseille fans after favouring a move to Nice last month, nearly squeezed a third through the legs of Lopez after Valentin Rongier misjudged a Schmeichel clearance.
Ukraine international Malinovskyi halved the deficit for Marseille with a thumping finish from a Clauss cut-back on the hour for his first goal since signing from Atalanta in January.
Schmeichel denied Clauss after a brilliant ball through from Jordan Veretout and Alexis Sanchez was unable to get a touch on Under's teasing cross as Marseille pressed for an equaliser.
Substitute Brahimi put an end to Marseille's bid for an eighth win in nine games when he advanced into the area and whipped superbly into the far corner.
- Lens lose ground on PSG -
Earlier, Jonathan Gradit scored a late equaliser in a 1-1 draw at Brest as Lens narrowly avoided suffering successive league defeats for the first time this season.
Jeremy Le Douaron turned home a low cross to give Brest the lead early in the second half but Gradit rescued Lens after goalkeeper Marco Bizot failed to deal with a cross.
Lens stay in third place behind Marseille on goal difference.
Monaco defeated Clermont 2-0 with goals from Guillermo Maripan and Breel Embolo as Nantes won away to Ajaccio by the same scoreline.
Reims extended their unbeaten league run to 14 games after a 0-0 draw at lowly Auxerre, while 10-man Strasbourg beat Montpellier 2-0 for their first home win of the season.
Angers finally halted their French top-flight record run of 13 straight losses by drawing 0-0 at Lorient, earning a first point since September.
Lionel Messi scored a superb second-half winner as a Paris Saint-Germain side missing the injured Kylian Mbappe and Neymar came from behind to beat Toulouse 2-1 on Saturday.