Florian Thauvin scored twice as Marseille beat Angers 3-0 in Ligue 1 on Friday evening while Nice dropped points in the title chase.
Playmaker Thauvin struck either side of Remy Cabella's goal as OM moved up to sixth in the table, pending St Etienne's Sunday clash with Metz.
Thauvin's first goal was outstanding, curled hard and low with the outside of his left foot from 30 yards after Dimitri Payet unusually opted not to shoot direct from a free-kick, instead disguising a square pass into Thauvin's path.
Cabella ran on to Payet's long pass and rounded keeper Mathieu Michel for the second just 20 minutes in as Rudi Garcia's side took control early on.
The third came in the 77th minute when Clinton Njie created the chance on the right, Morgan Sanson crossed to the edge of the six-yard box despite losing his balance and Thauvin tapped home.
Nice were forced to come from two down to draw 2-2 at home to Caen as they risked losing ground on title rivals Monaco and Paris Saint-Germain.
Ivan Santini's header put the visitors ahead and Yann Karamoh doubled the lead five minutes after half-time after a break from defence. His lob over keeper Yoan Cardinale sat up in the penalty area but Dante misjudged the bounce, allowing Karamoh to finish.
Dante redeemed himself by teeing up Nice's first goal for Mario Balotelli and Anastasios Donis struck in the 77th minute to at least salvage a point.