The Argentine international's effort condemned the Milan giants to a fifth straight defeat, plunging them further into crisis while the Azzurri climbed into the top five
Ezequiel Lavezzi grabbed the goal just before the hour mark, stroking a wonderful effort across Julio Cesar and into the far corner from the edge of the area to take his tally to four goals in three games over the past eight days.
The Azzurri had to see out the closing stages with 10 men after Salvatore Aronica’s sending-off, but Inter never looked like getting back level as they slumped to a fifth straight loss.
After Dejan Stankovic and Gokhan Inler exchanged early sighters, the game settled into a rather pedestrian pace in the opening quarter, with Napoli’s width giving Yuto Nagatomo and Marco Faraoni problems.
The first save of real note came on 24 minutes, when Julio Cesar had to go at full length to his left in order to keep out a stinging right-foot drive by Blerim Dzemaili. The Brazilian was then left standing moments later as Lavezzi swung in a magnificent free-kick from the right, but Edinson Cavani’s header wasn’t a clean one and just went the wrong side of the far post as a result.
Wesley Sneijder then came close to testing Morgan De Sanctis at the other end just before half-time. The Dutchman whipped in a wicked free kick which was just short of the necessary amount of curl, dropping agonisingly wide as the keeper scrambled to cover.
Claudio Ranieri made a very noteworthy double change at the break, replacing Sneijder and Diego Forlan with Ivan Cordoba and Giampaolo Pazzini. The switch meant an alteration in shape too, as a restructured Inter came out for the second half in a 3-5-2 formation.
But it was the Azzurri who made the first decent change after the restart, with Juan Zuniga’s cross from the left inviting Christian Maggio to head towards target, but the wing-back’s effort didn’t have enough on it and the ball flashed wide.
Inter failed to heed the warning, and with Napoli beginning to force themselves on their visitors, they soon took the lead.
Cavani picked up the ball and fed Dzemaili, who drove through the centre, holding off two men, before flicking a pass to Lavezzi. The ball didn’t run perfectly for the Argentine, yet he opened out his body and guided a beautiful shot inside the far post, leaving Julio Cesar with no chance.
As Inter looked to get back into the game, Pazzini made a good run to meet Nagatomo’s cross, but couldn’t adjust his feet quickly enough to get a shot on target.
They were given a boost in the 79th minute though, as Faraoni exposed Aronica at the back and was brought down by the centre-half. Referee Mauro Bergonzi had no doubt in his mind that it was a goalscoring opportunity, showing Aronica the red card.
However, the home side held out after Pazzini missed a free header from just seven yards with two minutes left on the clock, then an injury-time foul by Zuniga on the striker in the area went unpunished.
The win means Napoli climb up into fifth place after Roma’s heavy defeat to Atalanta earlier in the day. Inter, meanwhile, fall nine points off the podium, leaving them with much to do to claim a Champions League spot for 2012-13. They have now conceded 11 goals since they last scored themselves, intensifying speculation about Ranieri’s future.