Lorenzo Insigne defeated former Italian teammate Gianluigi Buffon from the point of keeping Napoli well in the hunt for a place in the last 16 of the Champions League, thanks to a 1-1 draw at his home in Paris Saint-Germain on Tuesday.
The PSG traveled to Stadio San Paolo looking to go better after keeping a 2-2 draw in the French capital two weeks ago.
But since Juan Bernat has won a dominating first-round performance from PSG to hit the open man by half-time, Insigne did not make a mistake when the guests received a penalty immediately after Jose Callejon was a sandwich in the area.
The result considers Napoli top of team C, level in points with Liverpool after their defeat 2-0 by Red Star Belgrade earlier on Tuesday.
But in comments to Sky Sport, coach Carlo Ancelotti warned that the qualifiers are still not safe.
"We have to fight until the end, we hold tight," said Ancelotti.
PSG is third, with just one point bad, leaving Buffon with ample faith in the last 16 chances.
"Paris played a great game, it was a good performance and I'm happy because I think we are on the right track," said Buffon at RMC Sport.
"The red star made us and Napoli a big favor earlier, but there are always to play in the final races.
"But I'm sure we're improving and every draw for us sends out an important message."
In what was the 512th appearance of Captain Marek Hamsik in Naples, Edison Cavani's former teammate played only a cameo role after Angel Di Maria's replacement for the last four hours.
He let Neymar and Kylian Mbappe pull the strings ahead for the visitors, who gave a strong first 45 minutes that demanding Napoli fans were disappointed all over.
The first real fear for Napoli came in 23 minutes when Mbappe ran into Neymar's loop to shoot a left half-volley volley sank just above David Ospina's line.
After Mertens cut straight Buffon's face after a good free kick, Kalidou Koulibaly rescued the Italians twice consecutively with a well-timed Mbappe game and a timely follow-up to prevent Mbappe from crossing Thomas Meunier.
At the other end, Callejon created the Insigne for a weak volley, which Napoli's weak middle sparked a court wide from Buffon's face.
But the Napoli fans were desperate a bit later with more Mbappe magic.
The pace of the World Cup star led him to a cross to the left and took Raul Albiol before sending an unstoppable cut to Bernat's path.
The Spaniard took a touch and, as he fell to the turf, he pushed his right leg to calm Osmpina.
An Ancelotti's semi-final speech seemed to have had the desired result when a much more enthusiastic Napoli appeared after space, with the 40-year-old Buffon returning the years with some nice savings.
The former World Cup winner first pulled Nichita Maksimovic's charming effort into safety before directing Mertens's attempt at the battle shortly afterwards.
Napoli had to score when the Mertens stunt test set Callejon to the right of Buffon's goal but the Spaniard trapped.
As PSG panicked in the back, Buffon sharpened the cross of the nearby Callejon series on the Mertens trail only to blow the Belgian from two yards.
Napoli fans were further disappointed when former Buffeton legend of Juventus stayed on its ground to violate Fabian Ruiz's first timer following the cross of Mertens.
Buffon was eventually defeated, but only from the point, from the 62nd minute of Insigne.
PSG coach Thomas Tuchel introduced Cavani for the final 14 minutes, while Mertens, who was holding an injured arm, was replaced by Adam Ounas.
The much-needed impetus for the attack failed to materialize for the PSG, which five minutes since Mbappe saw somehow wipe his strike from Thilo Kehrer's tradition from Osmpa upright when he reached eight yards from the goal.