Trailing at half-time to Milan Djuric's early header and loudly barracked by protesting away fans, champions Napoli roared back to win following sumptuous strikes from Victor Osimhen, Matteo Politano and Piotr Zielinski in six second-half minutes.
Andrea Colpani's deflected strike closed the gap to one seconds after Zielinski's first goal since October, but Giacomo Raspadori added the fourth in the 69th minute to ensure Napoli moved up to seventh.
Francesco Calzona's side will hand over their league title, almost certainly to Inter Milan, at the end of the season and are 10 points behind Bologna who currently sit fourth and in the last Champions League spot.
However, Serie A is leading the race for an extra place in next year's revamped tournament, meaning fifth could be good enough. Roma are three points behind Bologna in fifth after beating local rivals Lazio 1-0 for the first time in over two years on Saturday.
Two points ahead of Napoli in sixth are Atalanta who are at Cagliari later on Sunday and also have another game in hand to play with Fiorentina before the end of the season.
Osimhen drew Napoli level in the 55th minute with a towering header which briefly left the Nigeria forward in agony on the ground after landing awkwardly following his huge leap over Armando Izzo.
Two minutes later, Politano scored one of the goals of the season to put Napoli ahead, volleying home an unstoppable dipping shot from distance.
And Monza goalkeeper Michele Di Gregorio was left punching the air in frustration after failing to move for Zielinski's long-range rocket which crashed in off the crossbar. And Raspadori netted just 21 seconds after replacing Khvicha Kvaratskhelia to seal a rare convincing win for Napoli in a troubled campaign.
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