The Brazilian world record signing was handed a start by coach Unai Emery for the game in Brittany, two days after international clearance came through for his €222 million ($261 million) switch from Barcelona, AFP reported.
The 25-year-old, at home in PSG's all yellow change kit, played a part in the own goal scored by Jordan Ikoko that gave the away side the lead early in the second half.
He then set up the second goal for Edinson Cavani with a superb pass in behind the Guingamp defense before completing a comfortable victory with his team's third goal eight minutes from the end as PSG made it two wins from two to start the French season.
"People think that leaving Barca is to die, but no, it's the opposite," Neymar told reporters.
"I'm more alive than ever. I play, I'm very happy, and football is the same. Only the country, the city and the team change, but football is the same."
Guingamp coach Antoine Kombouare, a former PSG player, described Neymar as a "phenomenon".
"It's been a long time since I have seen such a phenomenon. All his teammates want to play with him and he brings competition," said Kombouare.
"Everyone gets more time because of him, he can accelerate and make a difference. We're happy that we don't have to play PSG every weekend."
Despite the many distractions of the last couple of weeks, including trips to China, Portugal and the French Riviera and glitzy presentations to the media and PSG fans, Neymar lasted the full 90 minutes.
He had taken the place of Javier Pastore in the Paris side in the only change from last week's 2-0 win over Amiens, completing a €350 million-front three with fellow South Americans Cavani and Angel Di Maria.
Neymar was one of four Brazilians in the PSG lineup, not including Brazil-born Italy midfielder Thiago Motta, for the game played before a sellout crowd at the 18,000-capacity Stade du Roudourou.
Guingamp, a sleepy little town 500 kilometres west of Paris with a population of barely 7,000, may have been a slightly incongruous setting for such an occasion but the match was broadcast live in more than 180 countries according to his new club.
That was a sign of the interest generated worldwide by Neymar's transfer, which Qatar-owned PSG hope will help them conquer Europe after so far coming up short in the Champions League in recent seasons.