The 52-year-old, who left the Partenopei to join the Nerazzurri in the summer, criticised the referee for sending off Ricky Alvarez as his side chased the game.
"It hurts me to lose a game we dominated, controlled and in which we attacked constantly," he told Sky Sport Italia. "Napoli were always forced to deal with our style of football.
"I complimented my players for their performance and I am proud of them. We are growing and now must work on our style of football, which today was exceptional. I told my men that if we always play like this, we will not lose many games.
"There was a series of terrible mistakes that changed the game. When we were in control and 3-2 down, Alvarez was harshly sent off. I think with 11 men against 11 we could've got back on level terms."
Inter are fifth in Serie A.