Following his world-record €222 million move from Barcelona, Neymar will make his Paris Saint-Germain debut on Sunday after being named in the starting XI to face Guingamp.
Cavani returned the favour with a flawless cut back and Neymar poked the ball home eight minutes from time.
With Unai Emery's side already leading 1-0 thanks to Jordan Ikoko's freakish own goal, Neymar assisted Edinson Cavani with a wonderful pass before the roles were reversed eight minutes from time for the Brazilian to tap home. Neymar then span a ball in for Marquinhos whose header came back off the post (35').
Neymar celebrates his debut goal.
After the first half finished 0-0, Jordan Ikoko scored a barely believable own goal seven minutes after the break.
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He also provided the pass which set up Edinson Cavani to put the French giants 2-0 up.
It looked as if that might be his most notable contribution, with Johnsson saving well to deny him towards the end, but within seconds of that effort Neymar finished Cavani's cutback.
The win sees PSG join four other clubs as the remaining teams with a 100% record after two league games.
Earlier, champions Monaco kept up their own impressive start to the new campaign with a convincing 1-4 victory away to Dijon - former Chelsea and Manchester United striker Falcao nabbed an impressive hat-trick while man of the moment Kylian Mbappe had to settle for a seat on the bench.