Benitez believes that his team were on top in the second period but found it difficult to break down the defensive home side.
"The penalty changed everything," Benitez told Sky Sport Italia. "Everyone told me it was not a penalty. You can see 50 of those tussles in every game. I am not here to say whether it was a penalty or not, as that will be down to the referees to judge.
"Up until the penalty we were pinning Roma back, but that changed everything and we went down to 10 men. If Roma defend with 11 men behind the ball, it's not easy to find space.
"I look at the performance and in terms of character Napoli did very well this evening. I said beforehand this game would not decide the title, but clearly with the way we played tonight I'd say it was a positive evening. We played well and this bodes well for the future."
Napoli now trail the leaders by five points in Serie A.