The Naples club, which went bankrupt in 2004 and had to be reformed in the lower leagues, will return to the European Cup next season for the first time since Diego Maradona helped them qualify by winning the 1990 Italian title.
Their San Paolo stadium was filled with blue smoke, Mazzarri burst into tears and club owner Aurelio De Laurentiis, a film producer who brought one on Italy's most fervently supported clubs back from the brink of extinction, was thrown in the air.
"Now we will create a squad able to compete in Europe, where you need experience to play against certain sides," De Laurentiis told reporters after his side had secured third spot.
Mazzarri, linked in the meida with once mighty Juventus has a rocky relationship with the owner despite Napoli's huge achievement and has not guaranteed he will stay.
"It depends only on him," De Laurentiis added. "He has a two-year contract, otherwise it will be a soap opera. But if he asks me to leave, I'll say no."
Napoli's success has partly been down to the shrewd purchase of Uruguay striker Edinson Cavani from Palermo before the season.
The previously goal-shy forward has bagged 26 league goals this term.
