Edin Dzeko struck a brace and Mohamed Salah added a third as clinical Roma dented Napoli's Serie A title hopes with a superbly-orchestrated 3-1 win at a shocked San Paolo on Saturday.
Napoli were looking to get back to winning ways after a shock defeat at Atalanta two weeks ago left them four points behind leaders and champions Juventus.
But the Azzurri never recovered from Dzeko's second goal of the game on 54 minutes and heads dropped when Salah beat Pepe Reina four minutes from the end.
Roma moved up to second at two points behind Juventus ahead of the Turin giants' match at home to Udinese later Saturday.
Napoli drop to third and could be seven points adrift by the end of the day.
Less than a week after seeing Polish striker Arkadiusz Milik sidelined for several months with a cruciate ligament injury, Sarri, as expected, opted for Manolo Gabbiadini as his key striker.
But the up and coming Italian, much like a disappointing Napoli was ineffective and replaced in the second half by Belgian Dries Mertens.
The 'Derby delo Sole' started in summer-like conditions and the hosts initially enjoyed a bright start, Lorenzo Insigne sending an early free kick just wide of Wojciech Szczesny's far post.
But despite showing early promise, Napoli came up short in front of goal and were clumsy in defence.
Dzeko was a concern for Napoli throughout and it took a great sliding tackle from Kalidou Koulibaly on the quarter hour to thwart the Bosnian after he pounced on Radja Nainggolan's first-time through ball.
Nainggolan sent Salah through on 21 minutes but the Egyptian's low snap shot curled wide of the upright and when Diego Perotti pounced on Koulibaly's fluffed clearance moments later the Argentine curled inches wide of Reina's far post, with the 'keeper at full stretch.
Roma were relieved when three Napoli shots in succession were blocked in the area, Callejon coming closest only for his shot to come off Kostas Manolas.
The visitors' defence stood firm again when Insigne turned inside Manolas to set up Marek Hamsik for a drive that came off Federico Fazio.
When Salah sent Dzeko in behind the Napoli defence, an alert Reina rushed out to bravely pluck the ball from his feet.
But the Spanish 'keeper had no chance in the 43rd minute.
Koulibaly panicked as Salah harried him at the byline, and when he fell on his behind the Egyptian pounced to deliver a cross that, after Nainggolan's dummy, an unmarked Dzeko swept past Reina.
An unrelenting Salah kept Koulibaly on his toes throughout the second half, but a nervous Sarri was looking for solutions shortly after the restart.
As Mertens warmed up to eventually replace the ineffective Gabbiadini, the Belgian international was cautioned for dissent whil still wearing his yellow bib.
Moments later, Napoli's woes intensififed, Dzeko holding off Elseid Hysaj at a free kick to head past Reina from the edge of the box on 54 minutes.
Napoli's title hopes took a direct hit, but three minutes later Koulibaly made amends for his earlier blunder by rising above the Roma defence to meet Ghoulam's corner with a glancing header that came off Szczesny's far post before finding the net.
Yet a Napoli fightback looked unlikely, and when Daniele De Rossi sent an unmarked Salah free down the right the Egyptian had time and space to pick his spot before beating Reina down low.