Neymar was left out amid ongoing speculation over his future, but Edinson Cavani, Kylian Mbappe and Angel Di Maria were all on target at the Parc des Princes.
Champions in six of the last seven seasons, Cavani got the ball rolling for PSG with a contentious first-half penalty that was followed by a well-taken strike from Mbappe.
Mbappe then turned provider by setting up substitute Di Maria for the third as Thomas Tuchel's men made a serene start to their latest title defence.
A calf injury prevented Ander Herrera from making his home debut, but fellow new signings Pablo Sarabia and Abdou Diallo were both handed starts.
The hosts' breakthrough arrived 24 minutes in through Cavani's penalty, awarded for a handball against Pablo Martinez.
Sarabia's whipped corner hit Martinez on the hand, but PSG's appeals were muted and play was allowed to continue for a further minute before the referee pulled play back for a VAR check.
Nimes goalkeeper Paul Bernardoni produced a flying save to keep out Sarabia's left-footed volley at the back post 10 minutes later, while Cavani failed to convert an Mbappe cutback from close range shortly before half-time.
But PSG gave themselves breathing space 56 minutes in thanks to Mbappe's sweet strike into the top left corner after being teed up by Juan Bernat.
And Di Maria rounded off the scoring four minutes after being introduced from the bench, picking out the bottom right-hand corner once played in by Mbappe.
What does it mean? Neymar saga turns sour
Neymar has not featured for PSG since last season and he was not part of the squad today, with sporting director Leonardo hinting this week a move away from the club - either to Real Madrid or Barcelona - could be close.
Certain sections of the Parc des Princes aimed derogatory chants towards Neymar before and during the match, but on the field Tuchel's men showed they can cope without the Brazil forward as Cavani, Mbappe and Di Maria all registered.
Mbappe up and running
The path is clear for Mbappe to become the undisputed star of this PSG side should Neymar depart, and he took just 56 minutes of the new campaign to get off the mark. He also linked up well with Cavani and teed up Di Maria for the third goal.
Verratti and Draxler let off the hook
Despite already being on yellow cards, Marco Verratti and Julian Draxler both produced strong challenges in the final 25 minutes of the game that could have led to their dismissal on another day.
PSG have an away game against a familiar foe next Sunday as they travel to Rennes, who they beat in the Trophee des Champions last week, while Nimes host Nice the day before.