Milan, who sit 10th in Serie A, are now winless in five outings, but Inzaghi insists that he has the core ingredients needed to turn things around next season.
"I have been able to turn everything around since taking charge last summer," the Rossoneri coach told Sky Sport Italia. "We had four great months and then we struggled.
"But there's something good there. The club will make their evaluations but I have a contract.
"But it was a game shaped by the dismissal. I saw a good team for 70 minutes. Maybe a yellow would have been fairer than a red, because Gabriel Paletta was also there."
Despite the numerical advantage, the Partenopei struggled to break down Milan's defence but struck gold on 70 minutes through Hamsik, before Higuain and Manolo Gabbiadini completed the scoring.