The forward got his 13th French topflight strike this term as the Great Danes faltered against Andre Villas-Boas’ Phocaeans
Despite his injury in the Great Danes’ win at Angers, Osimhen was handed a starter’s role in the hard-hitting encounter.
After a goalless first half inside Stade Pierre-Mauroy, the Nigeria international gave Christophe Galtier’s men a 51st minute lead.
The 21-year-old beat goalkeeper Steve Mandanda after controlling a defence-splitting pass from Jonathan Bamba.
16 minutes later, Marseille levelled matters as Mozambique international Reinildo Mandava turned the ball into his net.
Dario Benedetto had the final say two minutes later after converting Valere Germain’s assist to hand Andre Villas-Boas’ side all points at stake.
Osimhen’s effort was his 13th in the French elite division this term, and is now three goals adrift leading scorer Wissam Ben Yedder.
While he was in action for the entre duration, Cameroon’s Jean Emile Onana was replaced by Timothy Weah with 10 minutes left to play.
Following this setback, Lille remain fourth in the French elite division log with 40 points from 25 outings. They host struggling Toulouse in their next outing on Saturday.