AC Milan gained a narrow advantage over Napoli in the first leg of their all-Serie A Champions League quarterfinal on Wednesday night.
Milan's Algeria midfielder Ismael Bennacer struck the winner from the edge of the area after Braham Diaz broke superbly on the halfway line.
Napoli had midfielder Andre-Frank Zambo Anguissa sent off in the second half after a second yellow card and were well held by an organised Milan.
Milan also came close to a second goal when Simon Kjaer's header bounced off the underside of the bar.
"It is so important to have a positive result," Milan forward Diaz, named man of the match, later said.
"Not conceding a goal was great. We need to play to win next week."
The second-leg of this tie will be at Diego Maradona stadium in Naples next week.