Rhys Williams, Rafael Camacho (two), Bobby Adekanye and Curtis Jones scored the goals for Barry Lewtas’ side, who were simply too strong for the visitors from the off in St Helens.
The young Reds therefore set the pace in Group C of the competition, with Red Star Belgrade and Napoli playing out a 1-1 draw in the other fixture.
PSG’s patient control of possession in the earliest stages of the game gave way to an emphatic period from Liverpool that effectively settled the tie’s outcome.
An eighth-minute short corner routine that did not quite click was recycled by Jake Cain to Neco Williams and he swung in a perfect cross for namesake Rhys to take advantage of a free header and find the net.