Former transfer target Gonzalo Higuain scored for the visitors.
"I think Napoli are a very good side. Very well organised. I like what they did in midfield. You could see that this team plays for a few years together. Marek Hamsik was especially dominant in the first half," said Wenger.
"They gave us big problems there. Overall they are compact, united and a very well-organised team that is very good."