A second-half strike from Uruguayan hitman Marcelo Zalayeta demoted the Nerazzuri to their first league defeat in over three months.
"I am not angry, just disappointed, as you always prepare the match with the idea of winning," Mourinho said after the game.
"We will work within the squad on analysing this defeat and discussing what happened so we can get the nine points we need."
While admitting that his team didn’t deserve a win, Mourinho said that Sunday's clash was no more than a boring affair.
"To be honest, this match could have been played without any goalkeepers at all. It was played at a low tempo, with poor quality - mainly from us in the second half.
"Napoli scored a great goal out of nowhere. Admittedly if anyone deserved the luck to win tonight it was Napoli, because they put more intensity and ambition into it."
The Napoli loss means that the gap between Serie A leaders Inter and second-placed AC Milan decreased to seven points, and Mou was not happy when journalists reminded him of such fact.
"I don't need to know how far behind Juve or Milan are. I know where they are, but I do not need that information, all I need to know is that we require nine points.
"We have to focus only on ourselves for five rounds and that is a wonderful advantage to have," The Portuguese tactician concluded.