Marseille missed the chance to extend their lead at the top of Ligue 1 as Bernardo Silva scored the only goal of the game to give AS Monaco a 1-0 victory at Stade Louis II.
Florian Thauvin was a constant threat to the Monaco defence throughout the evening, and his inviting cross should have handed Marseille an early lead, but an unmarked Andre-Pierre Gignac could only head wide at the back post.
Despite struggling to enjoy as much possession as the visitors, Monaco did look dangerous in the final third, and they were inches away from breaking the deadlock when Anthony Martial rattled the crossbar.
However, Marseille continued to look the most likely to score first, and another chance came from the boot of Thauvin when Mario Lemina climbed highest to head his cross wide.
Danijel Subasic came to the rescue for Monaco as Marseille stormed forward early in the second half, with Gignac being left frustrated by the Croatian shot-stopper after he had combined with Dimitri Payet on the edge of the box.
The game's only goal arrived in the 67th minute when Yannick Ferreira Carrasco combined with Martial before pulling the ball back to Silva, who kept his composure to put Monaco ahead.
As Marseille went in search of a way back into the game, Monaco started to threaten on the break, with Lucas Ocampos testing Steve Mandanda with a powerful low strike.
There would be no late twist, though, as a dramatic day of Ligue 1 action finished with the top two suffering defeat.