The Azzurri lost a first league game since December 16 as goals from Boukary Drame and Cyril Thereau handed Chievo a 2-0 win - Napoli's third straight loss at the Stadio Marc'Antonio Bentegodi.
Edinson Cavani went on to miss a penalty as league leaders Juventus pulled nine points clear at the top with a 1-0 victory over Catania, but Mazzarri predicts a positive, and immediate, reaction from his players.
He told sscnapoli.it: "We have never been lucky in Verona. They scored on their first attempt and then we were out of it.
"Chievo are definitely our bete noire as we have not won here for three years. But every season brings moments like this and we must overcome them.
"We are still second in the table, we are playing in a great league and we are two points ahead of AC Milan.
"If you consider the glass as half full, we have done many good things. We have collected many more points than we had at this stage last year."
"The group is solid and the lads believe in themselves, and starting from next Sunday against Atalanta we will be ready to start afresh.
"A match like today's can happen but we know how to react. There are still many games to play and we can do well."
Chievo, meanwhile, took a significant step towards securing their place in the top flight as three more valuable points built an eight-point cushion on the relegation zone.
And Flying Donkeys head coach Eugenio Corini admitted taking tips from Juve, who secured a 1-1 draw at Napoli last week, when preparing his players for yesterday's game.
"We played well, especially in the first half," he told La Repubblica. "We left our opponents very little room to manoeuvre.
"I used a five-man defence after watching Napoli-Juventus and we've used a similar system to Juve in the last few matches.
"So I decided to take that approach again here and it paid off."