Two sublime strikes in the space of five first half minutes did the damage for Napoli. Had it not been for the heroics of Mariano Andujar in the Catania goal, the winning margin would have been far greater.
Catania suffered a double blow during their midweek drubbing by Juventus. Striker Gonzalo Bergessio broke his fibula and is out for two months, while Tiberio Guarente was sent off and was unavailable for this game. Nicolas Spolli, Giuseppe Bellusci, Pablo Barrientos and Jaroslav Plasil were also sidelined for the Elefantini.
Napoli were forced into an early change when Giandomenico Mesto succumbed to a knee injury after just seven minutes. The defender fell awkwardly and had to be helped back to the bench. Club captain Paolo Cannavaro was surprisingly overlooked in favour of youngster Bruno Uvini.
Pablo Armero and Hamsik exchanged passes for Gonzalo Higuain to head over an early warning, before the home side hit the front on 15 minutes. Higuain held the ball up long enough for Callejon to collect and blast into the top corner, giving Andujar no chance. Five minutes later, Lorenzo Insigne dribbled unchallenged along the 18 yard line. His lay off was curled expertly into the net by the waiting Hamsik.
Napoli were coasting, but let their guard down and paid the price on 25 minutes. Maxi Lopez backheeled for Castro to slot home from a Cristiano Biraghi pull back. The forward was given enough space to place a low shot past a static Pepe Reina into the bottom corner.
Norbert Gyomber blocked Higuain's shot on the turn four minutes before the break, after the Argentine collected Insigne's pass in the area.
Napoli laid siege to the Catania goal after the restart, but were thwarted by the brilliant Andujar. The goalkeeper kept Higuain's first time shot from going into the near corner after the forward was threaded through by Callejon. An unmarked Federico Fernandez wasted a free header, before Andujar tipped over a vicious Hamsik drive. The Slovakian midfielder blasted the ball straight at him.
On the hour, Andujar blocked Higuain's shot with his legs. Tachtsidis was alert to clear a Hamsik effort from point blank range, when one of the home side's many corners wasn't cleared properly.
Andujar denied Raul Albiol with his legs after the Spanish defender nodded down Insigne's free kick. Late on, Nicola Legrottaglie played Higuain onside, only for the frontman to drag his shot wide. Gyomber then inexplicably moved out of Callejon's way, giving the Spaniard a clear view at goal, but he wasted his effort from 18 yards.
The most Catania could muster was a tame Castro header, which was easily caught by Reina.
Napoli: Reina; Mesto, (Uvini 7) Fernandez, Albiol, Armero; Dzemaili, Behrami; Insigne, (Mertens 90) Hamsik, Callejón; Higuain (Zapata 79)
Catania: Andujar; Alvarez, (Rolin 83) Gyomber, Legrottaglie, Capuano; Izco, (Petkovic 71) Tachtsidis, Almiron, Castro, Biraghi; (Keko 46) Maxi Lopez
Goals: Callejon 15 (N) Hamsik 20 (N) Castro 25 (C)