Wins for both Lens and PSG left Marseille knowing they could not afford to slip up if they wanted to keep themselves within touching distance of the leading duo, and they certainly started with intent here.
Within six minutes, Lukas Hradecky was required to produce an incredible save to deny Pierre-Emerick Aubameyang’s stab towards goal, before Timothy Weah had a shot saved by the Finland international. Mason Greenwood also pulled a shot wide in what was an opening half-hour that belonged to the Phocéens.
Monaco responded well, and by the time the half-time whistle came around, they were well on top. First, Aleksandar Golovin and Maghnes Akliouche had shots saved by Geronimo Rulli, before the Argentine also thwarted Takumi Minamino.
The best chance of the half fell to Folarin Balogun, who would have scored the game’s opening goal had Pierre-Emile Hojbjerg not produced a last-ditch goalline clearance shortly before the break.
The second half, much like the first, was an end-to-end affair, with both teams having numerous opportunities to break the deadlock. Minamino was through on goal inside 15 seconds of the restart, but could only push his low effort just past the post.
Monaco even had the ball in the net around the hour mark when Lamine Camara hammered into the corner, but the goal was ruled out for an offside in the build-up.
At the other end, Greenwood almost found the top corner from distance, instead just missing the target, before Hradecky leaped to keep out Aubameyang's effort.
This was turning into a breathless encounter, and after Minamino had another shot saved, Monaco had the ball in the back of the net for a second time through Balogun.
Once more, however, it was ruled out for offside, and Marseille soon took advantage of that second reprieve, driving down the pitch prior to Greenwood sweeping into the top corner from just inside the area to score for a second successive home head-to-head.
Much in keeping with the rest of the game, Monaco continued to push forward, but Marseille had the incentive to take the sting out of the game and did just that, seeing out the game to pick up a valuable three points and stay within five of Lens at the summit.
Monaco, meanwhile, have now lost five of their last six Ligue 1 games to drop down to ninth, a whopping nine points adrift of their hosts here.
Flashscore Man of the Match: Lamine Camara (Monaco)