Lorenzo Insigne punished a Thiago Silva error from the penalty spot after 61 minutes to hand the Italian side leadership of Group C following Liverpool's earlier 2-0 loss to Red Star Belgrade, Napoli's next opponents.
Gianluigi Buffon, making his Champions League debut for PSG, had made several saves to preserve a lead earned by Juan Bernat, but his foul in attempting to atone for Silva's loose touch allowed his former Parma boss Carlo Ancelotti to have the last laugh.
Edinson Cavani's late introduction against his ex-employers failed to provide the inspiration PSG needed to convert a point into something more valuable to their hopes of advancing.
Neymar was lively in the opening exchanges and carved out a promising early chance for Marco Verratti, which drew Kalidou Koulibaly into a crucial block.
The Brazil star also provided the pass for a thumping Kylian Mbappe strike that flew across the face in the 23rd minute.
For all their attacking riches, PSG had wing-back Bernat to thank for breaking the deadlock with a composed close-range finish, Mbappe having bamboozled Raul Albiol before supplying the cutback.
17 - Kylian Mbappe is involved in 17 goals in his last 18 Champions League games (12 goals, 5 assists). Unleashed. pic.twitter.com/DGDt0F9knv— OptaJean (@OptaJean) November 6, 2018
Napoli started the second half with purpose but ran into an inspired Buffon, who twice denied Dries Mertens in quick succession.
Eventually, the incessant Napoli pressure told. Buffon bore little blame for clattering into Callejon and, with lasers shone in his eyes, could do nothing about the emphatic Insigne spot-kick that put Napoli in the driving seat.
There was some late frustration for the hosts as they lost Mertens to a serious-looking shoulder injury in a match that saw Marek Hamsik become the club's all-time appearance leader.
What does it mean? PSG fail to dispel flakiness fear
Accusations of a soft centre have long been levelled at PSG and, though they clung on here for a handy point, their inability to see through a period of pressure will only heighten the focus on the team's character.
Callejon showcases class
He was frustrated in his attempts to get on the scoresheet, but attacker Callejon deserves plenty of credit for pouncing on Silva's error as the most important moment of a consistently dangerous display.
Silva slip-up costs PSG
Silva will receive no sympathy for the error which came from nothing and handed Napoli their equaliser.
Key Opta Facts
- Of sides they have faced at least four times across all European competitions, against only Real Madrid (0/4) and now PSG (0/4) have Napoli failed to win any of their first four meetings against a single opponent.
- PSG's tally of five points from their opening four matches of this season's Champions League is their lowest total at this stage since 2004-05, the last time they failed to make it out of the group stages.
- Napoli's Lorenzo Insigne has scored in each of his last five home matches in the Champions League (seven goals), becoming the first Italian player in the competition's history to achieve this feat.
- PSG forward Kylian Mbappe has been directly involved in 17 goals in his last 18 Champions League games (12 goals, five assists).
- PSG goalkeeper Gianlugi Buffon (40y 282d) has become the second oldest player to make their Champions League debut for a club after Mark Schwarzer (41y 65d), when he turned out for Chelsea back in December 2013.