The visitors bossed possession in the first half, but it was their relegation-threatened opponents who enjoyed the first shot on target, as Zuriko Davitashvili’s low strike was well parried away by Geronimo Rulli.
At the other end, Mason Greenwood’s tame effort straight at Gautier Larsonneur was an anticlimax, but the Olympians finally struck gold on 17 minutes, when Valentin Rongier fed Neal Maupay.
The former Everton man’s gorgeously lofted reverse pass found Adrien Rabiot, who produced a cool chest-trap before thumping in on the volley.
The goal was initially ruled out for offside against the former Juventus midfielder, before being overturned by VAR.
Not long after his opener, Rabiot could have doubled Marseille’s advantage, just failing to make clean contact with Luis Henrique’s fizzed cross. Maupay then should have pulled the trigger when put through by the composed Pierre-Emile Hojbjerg, only to be tackled brilliantly by Yunis Abdelhamid, before Larsonneur repelled Quentin Merlin and Greenwood.
Roberto De Zerbi no doubt headed in at half-time much the happier of the two managers, but the Italian must also have felt that his men should have been further in front.
Whatever was said in the dressing rooms, Marseille remained in control after the interval, and although Maupay couldn’t turn in Henrique’s low cross, Greenwood was caught in the box just after the hour by Leo Petrot, leading referee Jerome Brisard to award a penalty.
The Englishman saw his initial effort excellently saved by Larsonneur, but he stayed calm to tuck in the rebound for his 10th league goal of the season.
De Zerbi’s opposite number Olivier Dall’Oglio subsequently made several substitutions, including the introduction of Saint-Etienne’s top scorer last term, Ibrahim Sissoko.
But the changes had no real impact. In fact, the hosts’ only real moment of note from there came from their fans, as smoke from pyrotechnics set off in the stands caused a short delay near the end of the game.
Les Verts now find themselves in the bottom three after a bad set of results for them across the league over the weekend. Contrastingly, Marseille are now just five points behind leaders Paris Saint-Germain and have the chance to cut the gap further at home to Lille next Saturday.
Flashscore Man of the Match: Adrien Rabiot (Marseille)