The Partenopei have lost their last three games, but Benitez has urged his players to rediscover their confidence ahead of Monday night's Serie A match against Lazio.
"We've had the best start to a season in our history. It has been very positive and, though we got a few games wrong, that just gives us more motivation to do better," he told reporters.
"I heard someone say our fitness levels are dropping, but we have run more in the last two games than in others. Perhaps we lost balance at times or our control over possession.
"We've lost three in a row, but two of them were against top level teams and aided by an offside and a penalty. We only drew one game this season, which shows we always want to win and I prefer to win one rather than draw three."
Napoli are currently third in the Serie A table with 28 points.