Arkadiusz Milik marked his full Napoli debut with a double before Jose Callejon's late brace claimed a 4-2 Serie A victory over nine-man AC Milan.
The former Ajax striker - signed to replace Gonzalo Higuain - opened his Napoli account just 18 minutes into his first start for the club, before adding another with a thumping header just after the half-hour.
With Milan having picked up just two points from their last five trips to Napoli, their prospects seemed bleak, but a whirlwind five minutes early in the second half saw excellent strikes from M'Baye Niang and Suso haul Vincenzo Montella's side level, while Napoli boss Maurizio Sarri was sent to the stands for protesting to the officials.
However, Napoli overcame their manager's absence, and found themselves back in front when Callejon tapped home from close-range following superb work from Dries Mertens.
And any hopes of another Milan comeback were ended when Juraj Kucka and Niang received their marching orders, before Callejon added a fourth in stoppage time.
Milan manager Montella got his tenure off to a winning start against Torino on the opening day, and his side went close to taking an early lead here - Chelsea target Alessio Romagnoli having a goal disallowed for offside after Ignazio Abate had somehow fired wide from close range.
Milan were made to pay for that miss when Dries Mertens, restored to the Napoli line-up following his brace from the bench against Pescara last time out, curled a superb strike against the post.
The ball rebounded straight into the path of Milik, who duly gave Napoli the lead despite scuffing his finish into the ground.
Mertens continued to look sharp, and the Belgium winger twice went close to extending Napoli's lead - only to be denied by two fantastic saves from Gianluigi Donnarumma.
However, Milan's goalkeeper could do nothing to prevent Milik doubling his tally in the 33rd minute, the Poland striker losing his marker to head home from Callejon's corner.
Milan came out on the front foot after the restart, and they found a way back into proceedings in the 51st minute, Niang lashing a low but powerful finish past Pepe Reina.
Napoli were adamant that there had been a foul in the build-up, and matters were made worse when, tired of Sarri's protestations, the referee sent the hosts' manager to the stands.
The goal sparked Milan into life and, just moments later, Suso completed the comeback with a blistering strike from the edge of the area.
But Milan's hard work was undone in the 74th minute. Mertens was again the instigator as Donnarumma parried his effort into the path of Callejon, who made no mistake from close-range.
Milan's task was soon made harder when Kucka picked up two yellow cards in quick succession for a foul on Mertens before kicking the ball away in frustration.
Niang was also sent off for a second bookable offence, for attempting to halt Reina distributing the ball quickly, with Callejon then doubling his tally - despite Romagnoli using his hand in an attempt to prevent the ball going over the line - late on to wrap up the points.