A first-half flurry from the Serie A hosts secured their top-flight future while simultaneously leaving the Partenopei in top-three limbo
Napoli's surge towards Serie A's Champions League spots was halted on Thursday as they went down 4-2 at Empoli.
Three consecutive wins had left Rafa Benitez's side five points off third-placed Roma ahead of their game in hand at the Stadio Carlo Castellani.
However, the Spaniard could only watch on in horror as a woeful defensive showing - including two own goals - led to a sound beating.
Empoli captain Massimo Maccarone opened the scoring with a fierce low shot in the eighth minute before Riccardo Saponara's cross ended up in the net after Napoli goalkeeper Mariano Andujar's parry cannoned into Miguel Britos' face to double the advantage in comical fashion.
It was three before the break via Saponara, the former Milan man acrobatically turning home on the rebound after Andujar thwarted Manuel Pucciarelli.
Vincent Laurini scored a carbon-copy own goal with 25 minutes to go, giving Napoli hope of a comeback.
But those ambitions were extinguished 10 minutes from time as another clumsy own goal, this time from Raul Albiol, left Andujar stranded.
Marek Hamsik lashed the game's best goal past Luigi Sepe in stoppage time but it was scant consolation for Benitez.
Victory takes Empoli up to 15th in Serie A, mathematically out of the drop zone's reaches after an impressive campaign back in the top flight that has seen them lose just nine times so far.