After failing to win on their travels since November, Inter finally ended their away day blues with a solid win in Florence thanks to goals from Rodrigo Palacio and Mauro Icardi.
But, while admitting that the result was impressive, Mazzarri was critical of his side for not putting the game out of Fiorentina's reach.
"Tonight we did well, but we also risked throwing away two points, as we waste too many chances," he told Sky Sport Italia.
"Against a quality side like Fiorentina, they can score at any moment and nearly did at the death.
"We've got to improve in certain respects, as we are too naive and at times were lazy, giving away corners that could've cost us the game.
"Near the end we almost conceded on the counter from our own free kick. It's absurd and we've got to grow up."
Mazzarri was not entirely negative though, and said he wants to see his side convert more of their opportunities in the future.
"As for the rest, I was really impressed with the first half and if we'd made more of our chances then it could've been a bigger result with less suffering," he added.
"When we are in good shape and play the kind of football I like, with the wingers attacking, it is closer to my idea of Inter.
"Considering where we were playing and who we were taking on, it was a great performance."
The win moves the fifth-placed Inter to within five points of Fiorentina, who sit fourth.
