Ranieri's first game in charge at the San Siro ended in defeat, as goals from Campagnaro, Maggio and Hamsik condemned the Nerazzurri to another home disappointment
Claudio Ranieri's home debut as Inter coach ended in embarrassment as goals from Hugo Campagnaro, Christian Maggio and Marek Hamsik gave Napoli a 3-0 victory to move the hosts, if only temporarily, to the top of the Serie A table.
A red card for Joel Obi, as well as boss Ranieri himself being sent to the stands, mean the 2010 treble winners are still without a win, or even a goal, at the San Siro this campaign.
Inter nearly took the lead early on, though, as Pazzini pounced on a spilt ball from De Sanctis to tap in from three yards. Unfortunately for the hosts, the Italy striker was judged as offside and the goal was, rightly, disallowed.
Lavezzi perhaps had the best chance of the first half an hour as a cross from Juan Zuniga found the Argentine who had his glancing header saved by Julio Cesar on 30 minutes.
The deadlock was broken on 40 minutes as a superb run down the right-hand side by Christian Maggio was halted by Joel Obi, who was controversially adjudged to have pushed the midfielder inside the box.
A penalty was given and a second yellow card brandished to the Nigerian. The resulting penalty from Hamsik was saved, but Campagnaro was there to fire in the rebound and give the visitors a 1-0 lead at half time.
That man advantage was starting to show after the break, and Maggio reinforced Napoli's dominance on 55 minutes. Hesitation from Nagatomo meant that the Italian could nip in 18 yards out, and chip the ball over the on-rushing Julio Cesar to give the visitors a two-goal advantage.
And things got even better for the visitors on 75 minutes. A through-ball from Lavezzi dissected the Inter defence, and Hamsik was on hand to calmly slot the ball into the net from 12 yards out.
The win leaves Napoli top of the table on 10 points whilst Inter languish just outside the drop zone on four.