Mauricio Isla scored the lone goal of the contest in the 73rd minute after he finished off a pass from Antonio Floro Flores inside the penalty area.
But the match didn't really come to life until the final 10 minutes as both teams missed a penalty kick and had a player sent off.
Inter's Javier Zanetti brought down Kwadwo Asamoah inside the penalty area to earn himself a red card and give Antonio Di Natale a chance to double his team's advantage.
Pazzini stepped forward to take the kick but he slipped as he was about to strike the ball, sending it over the crossbar.
Ferronetti picked up a second yellow card for arguing with the referee, but Inter failed to capitalize in the final minutes.
Napoli 4, Lecce 2
Napoli jumped out to a 3-0 lead at halftime with goals from Ezequiel Lavezzi, Cavani and Blerim Dzemaili in the first 40 minutes.
Luis Murial pulled a goal back for Lecce early in the second half, but Cavani netted his second goal of the match before a late tally from Lecce's Daniele Corvia.
Napoli moves into fifth with the win while Lecce has lost its last three games and sits on the bottom of the league.