Fresh from victory over Fiorentina in the Coppa Italia final on Saturday, Rafael Benitez's men were assured of third spot earlier in the evening when Fiorentina, in fourth, were stunned 4-3 by Sassuolo in Florence. Napoli went on to outclass their visitors from Sardinia, who played much of the second half with ten men after goalkeeper Marco Silvestri saw red for a foul on Goran Pandev on 54 minutes.
By then, Napoli had already raced to a 2-0 lead thanks to Dries Mertens' 33rd-minute spot-kick after Daniele Conti had hauled Pandev down in the box as the striker prepared to strike. Pandev doubled Napoli's lead three minutes before the interval when he turned Jose Callejon's unselfish square ball into a virtually empty net after the Spaniard had intercepted defender Davide Astori.
Despite having little to do, Napoli 'keeper Pepe Reina had suffered a slight muscle problem and, with number two Rafael also injured, was replaced for the second half by Roberto Colombo, the 38-year-old making his first official appreance for the Azzurri. Cagliari 'keeper Silvestri was at fault nine minutes after the restart when he brought Pandev down in the box as the Macedonian prepared to round him and shoot.
Cagliari coach Ivo Pulga took off Agim Ibraimi and sent on 'keeper Vlada Avramov, who was only too happy to see Marek Hamsik smash his spot-kick off the underside of the bar. Barely five minutes later, however, Blerim Dzemaili put the match beyond reach when he drove home Napoli's third.
Berardi hat-trick moves Sassuolo out of drop zone
Earlier, Domenico Berardi scored his second hat-trick of the season as Sassuolo stunned hosts Fiorentina 4-3 to move two points clear of the drop zone.
Sassuolo's eighth win of the campaign moved them up to 16th, two points clear of Bologna. Fiorentina remain fourth but with two games remaining Vincenzo Montella's side are only six points ahead of sixth-placed Torino.
Berardi gave the visitors a 23rd minute lead after Davide Biondini's shot came off the elbow of Borja Valero, who had tried in vain to twist away. The referee awarded a penalty and Berardi stepped up to beat Antonio Rosati.
Sassuolo were soon 2-0 up Nicola Sansone set up Berardi to beat Rosati at the keeper's near post. Simone Zaza's long-distance rocket then came off the top of the upright but Berardi claimed his hat-trick on 42 minutes when he danced around Stefan Savic to beat Rosati with a shot from a tight angle.
A brief Fiorentina fightback began just before the hour when Gonzalo Rodriguez beat Gianluca Pegolo from the penalty spot. But Sassuolo were soon celebrating again. Moments after Zaza had wasted a great chance, Sansone scored a fine individual effort from close range.
Italy striker Giuseppe Rossi, who returned from a fourth-month injury lay-off in a 20-minute substitute appearance during the Cup defeat on Saturday, came off the bench to make his league comeback and soon had his 15th goal of the campaign after combining with Valero and Fernandez to beat Pegolo with ease.
Minutes later Cuadrado ran on to a long ball from midfield to send a lob over the onrushing Pegolo for Fiorentina's third. Fiorentina spurned several chances to level in the dying minutes, notably when Rossi saw an injury-time volley tipped around the post.