Algeria midfielder Ismael Bennacer lashed in the decisive strike five minutes before half-time of an engaging contest at a packed, loud and wet San Siro after Brahim Diaz and Rafael Leao combined brilliantly.

The 25-year-old's strike ensured Milan's second win over Italy's champions-elect Napoli in less than a fortnight and a narrow lead to defend at Stadio Maradona in Naples next week.

Napoli, who had Andre-Frank Zambo Anguissa sent off in the 74th minute, should have Victor Osimhen back for the second leg on Tuesday and without their star striker Luciano Spalletti's team got nothing despite having plenty of chances.

Milan goalkeeper Mike Maignan made a series of impressive stops, in particular during an early salvo from Napoli which led to four good opportunities in the opening quarter of an hour.

He also saved Milan late on when he clawed out Giovanni Di Lorenzo's effort just as the more than 70,000 home fans were celebrating victory.

But Bennacer's strike was just enough to give Milan hopes of their first Champions League semi-final since they were crowned kings of Europe for the seventh and most recent time in 2007.

That prospect will be all the more mouth-watering for Milan fans as their likely opponents would be local rivals Inter following their convincing win at Benfica on Tuesday.