Olivier Giroud emerged as the hero for Milan, tapping in the decisive goal just before half-time after a blistering run from Rafael Leao, who once again proved instrumental in Milan's victory.
Giroud's goal redeemed him after he had missed a penalty earlier in the match.
Milan's win sets up a tantalizing local derby in the semifinals, as they are likely to face off against their city rivals, Inter Milan, who hold a two-goal advantage over Benfica ahead of their second leg on Wednesday night.
This historic achievement marks Milan's first appearance in the Champions League semifinals since their last title-winning campaign in 2007 when they were crowned kings of Europe for the seventh time.
Manager Stefano Pioli's tactical acumen and the team's solid performances throughout the tournament have earned them well-deserved praise.
On the other hand, Napoli, who have been enjoying a stellar season and are on the verge of their first league title since 1990, bowed out of the Champions League in a disappointing manner.
Despite Victor Osimhen's stoppage-time goal, Napoli's struggles in front of goal and Khvicha Kvaratskhelia's missed penalty proved costly, resulting in their defeat.
As the road to the Champions League final narrows, Milan's remarkable journey continues, and fans are eagerly anticipating the highly anticipated derby clash against Inter Milan in the semifinals.