Napoli coach Maurizio Sarri felt his team switched off during the second half of their 2-1 win over Inter on Monday.
Gonzalo Higuain opened the scoring early on at Stadio San Paolo before Inter defender Yuto Nagatomo was sent off before half-time.
Higuain struck again after the hour-mark, but Adem Ljajic pulled one back for Inter before Napoli held on.
Sarri said his team failed to put Inter away as the three points sent them above Roberto Mancini's men and into top spot in the league.
"We did well not to get discouraged during a difficult moment, so we must do equally well not to get ahead of ourselves now," he told Sky Sport Italia.
"Until the Inter goal we were dominating. In my view we considered it to be a done deal when 2-0 up and got distracted, making the kind of mistakes we don't usually do.
"In my opinion, I sensed anxiety."
Higuain's brace took him to 10 Serie A goals this season, including seven in his past seven league outings.
Sarri said the Argentina international was still capable of going to another level.
"It depends on him," he said.
"If he can take a step forward from a mental point of view, he can become better."