The Partenopei coach could see no reason why the referee ruled out the striker's goal during the early stages of the second half of the game at the San Paolo
The Partenopei were trailing to an own goal from goalkeeper Morgan De Sanctis when Edinson Cavani netted early in the second half.
However, referee Domenico Celi had already blown for an alleged foul by Christian Maggio in the build-up, leaving Mazzarri infuriated.
“I did not understand why that goal by Cavani was disallowed,” the Partenopei boss told Mediaset Premium shortly after the full-time whistle. “It would have been 1-1.
“[But] we will close the referee debate. I hope the next game such episodes will go more favourably for us.”
Celi’s ruling proved key as Roma went 2-0 up soon after through Pablo Osvaldo and even though Napoli gave themselves a lifeline on 81 minutes when Marek Hamsik struck, Roma secured the win with a late goal from Fabio Simplicio.
The hosts had been expected to prevail over a side which has struggled for confidence and consistency in recent weeks but Mazzarri insisted that he had always expected a tough game from Luis Enrique's troops.
"Roma are a good team,” he said. “We knew the dangers of this game. [But] I have nothing to admonish my Napoli over.
“I'm pleased by the performance of my boys. We accept the defeat. In football, you win and you lose.”
The loss will only add weight to the argument that Champions League participants Napoli are currently ill-equipped to compete on two fronts and therefore must strengthen during the January transfer window.
However, Mazzarri insists that he will not be pressurised into making any moves in the transfer window next month.
“January? I’m not even thinking about it,” he insisted. “I am still only running over tonight’s games.
“The result does not reflect how the game went. [But] Roma has a very strong squad. [Erik] Lamela is destined to become a champion. "
Napoli’s defeat means that they remain sixth in the Serie A table, with a resurgent Inter having moved above them with a narrow win over Cesena earlier in the day.