Carlo Ancelotti owned up to mixed feelings after Angel Di Maria's stunning equaliser prevented Napoli from claiming a precious Champions League victory.
Napoli had twice led through Lorenzo Insigne and Dries Mertens at the Parc des Princes and were good value for their advantage in the French capital.
But in the third minute of injury time Di Maria, who was part of Ancelotti's Champions League-winning team at Real Madrid in 2014, unleashed an unstoppable left-footed drive to save PSG and secure a 2-2 draw.
"We had almost won and are happy with the performance, but are angry and regretful at conceding at the 93rd minute," Napoli boss Ancelotti told Sky Sport Italia.
"Di Maria can create a shot into the far top corner at the last minute, that's what happens when you have that much quality in the side."
Napoli were the better of the two sides after drawing PSG's early sting, with Mertens striking the crossbar before Insigne opened the scoring with a delicious 29th-minute chip.
But the draw allowed Liverpool, 4-0 winners at home against Red Star Belgrade, to take over top spot in Group C.
"We had more spaces and could have finished better," said Ancelotti, who spent 18 months in charge of PSG boss before joining Real in 2013.
"But we were too sluggish, especially towards half-time.
"I had a wonderful period here and am always happy to see these players again.
"Now we await them in Naples. I think the second leg will be decisive for qualification from this group.
"We're playing on home turf and I think that'll be an extra bonus."
PSG owed their first equaliser to a slice of huge fortune when Mario Rui put through his own net just after the hour-mark.
They now trail Napoli by one point ahead of the return game at the Stadio San Paolo on November 6.
"I knew it was going to be super-complicated," PSG manager Thomas Tuchel said in comments reported by L'Equipe.
"We are not the favourites, everyone wants to believe that, but it is so.
"It's super-complicated this group, and we can not be surprised.
"This match against Naples lasts 180 minutes and it is half-time."
PSG's much-vaunted strikeforce of Neymar, Edinson Cavani and Kylian Mbappe made little headway against Napoli's resolute defence.
And Tuchel said: "We must improve tactically, but also in our head, and respect the importance of our possession and our position.
"We said at half-time that we had lost our structure, we did not play together for half-an- hour.
"In the second half, though, it was completely different."
