Monaco ended a bad week on a low with a 2-1 loss to Lille in Ligue 1 on Saturday as Marseille came badly unstuck at Auxerre.
Hakon Haraldsson's first half double earned Lille the points that lifted them above Monaco and Nice and into provisional third place and automatic qualification to next season's Champions League.
Adi Huetter's Monaco, who had started the season in such encouraging style, slipped to fifth days after being knocked out of the Champions League by Benfica.
Nice have the chance to overtake Lille when they host Montpellier on Sunday.
Marseille came back to earth with a bump after last week's 5-1 thumping of Saint-Etienne, crashing to a 3-0 defeat at Auxerre.
Gaetan Perrin opened the scoring and a double from Brazilian captain Jubal did the damage to move Auxerre up to 10th.
The loss left south-coast giants Marseille second on 46 points, 10 points behind Paris Saint-Germain.
Scuffles between rival fans before kick-off left 14 injured, two requiring hospital treatment, local authorities told AFP.
At Lille, Haraldsson opened the scoring on 22 minutes with a left-footed angled shot, the Icelandic winger adding a second three minutes from the break, with Takumi Minamino reducing the deficit in first half stoppage time.
Lille held on to put a spring in their step ahead of next week's trip to the Parc des Princes to face PSG, and then their Champions League last 16 clash with Borussia Dortmund.
At the start of the season Monaco were unbeaten and level with PSG after the first eight games.
Inconsistency then struck the Principality side with Saturday's loss their seventh from their last 15 league outings.
Elsewhere Saint-Etienne drew 3-3 with Angers.
On Sunday PSG go in search of their 18th win of the season at Lyon where victory will take them 13 points clear at the top.
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