"We made two mistakes from set plays, including an own goal, and we are suffering because we make mistakes we should not be making," Benitez told Sky Sport Italia.
"This result means we still have to improve, as I've said many times. We should be in control of a match and then we make a mistake. We are the ones who make the errors and we have to do better.
"Of course, we all expect Napoli to be at the level they were at early in the season and for the side to have more points by now. We cannot be satisfied with this and I am the first to be unhappy."
Napoli are now eight points adrift of Serie A leaders Juventus.