A late Lucas Castro header proved the winner.
“We are very disappointed with the result, but it was not a bad performance at all," Ancelotti told Sky Sport Italia.
“We allowed Cagliari very few counter-attacks, hardly any. At the end, we were taken by surprise, as we stopped to complain about a foul on Fernando Llorente and allowed ourselves to be caught cold off balance.
“It was paradoxical that (Kalidou) Koulibaly was sent off for saying something to the referee and we had a series of yellow cards, when if there was a team that was playing rough, it was Cagliari.
“I won't have this overall performance reduced to once incident. Napoli played very well. We could've done better, but that's always true in every situation. I do not judge games only on the results and I won't accept that attitude.
“Seeing as you are so desperate to find something to criticise, fine, I'll say we are sobbing when looking at the table. Happy? I am not remotely worried, not at all."