After going five games without a goal following his £60 million ($69 million) move from Everton, Richarlison got off the mark with a pair of clinical headers to break Marseille's resistance in north London.
Antonio Conte's team were well below their best for long periods, but the game finally swung their way when Marseille's Chancel Mbemba was sent off for a foul on Son Heung-min early in the second half.
That was Richarlison's cue to seize the spotlight as the 25-year-old netted with 14 minutes to play and struck again five minutes later.
Making the first European appearance of his career, Richarlison's predatory finishes showed why Conte made him his marquee summer signing.
The sight of the Brazilian weeping with joy as he celebrated with his family in the stands after the final whistle underlined what it meant to him.