Racing spent the last week training in Switzerland ahead of their Top 14 kick-off against Brive next Saturday and their new star teed up the first try with a delicious cross-kick for Adrien Plante to touch down.
But Sexton, who started all three of the Lions Tests against Australia, scoring the tourists' crucial second try in the decisive third, at one stage thought he was going to be fed a goldfish as part of his initiation to the Paris-based club - until the doctor vetoed it.
"We were going to have to eat them until the doctor intervened, I'm glad that he did intervene," he told the Irish Independent.
"We had plenty of other stuff for the initiation, but it was good. It got us into the environment.
"I played my first 40 minutes, I was delighted to get playing with the lads.
"There was some good stuff in the first half, some not so good stuff and we'll need to improve before playing against Brive next week."