The Azzurri were a class above in the triumph.
"We played against a side where all XI work hard, even those on the bench were working," said Ranieri.
"We only had one chance in the first half when it was still goalless, then the game was in Napoli's hands and they played better than us.
"We have to put up our hands and compliment them, recognising they put in a much, much more determined performance.
The Scudetto ambitions are now over, though the Giallorossi are in the Champions League and the Coppa Italia.
"I don't think a single game can cancel out a year and a half of work. We mustn't be downhearted, just as we weren't jumping for joy before. This season we have some difficulties and are not having the same run as last year, but we won't give up.
"Now we have to focus on Shakhtar Donetsk, another side who work hard and have some excellent individuals."