The two rivals are both battling for a spot in this year's final against reigning champions Real Madrid or Manchester City.
Milan and Inter play each other at least twice a season in Serie A, and now meet in the Champions League for the first time since 2005.
As both sides lined up on the pitch at the famous San Siro, the competition's anthem was played.
Fan passion was clear to see and hear as supporters cried 'the Champions!', as is often the case in Italian Champions League matches, at the end of the music.
Excitement and anticipation had been building way before, and Milan legend Clarence Seedorf revealed how special the stadium is.
Speaking to BT Sport, he said: "I always considered this one of the best stadiums in the world.
"Not because I played here but the atmosphere it created and the type of Italian fans, how they're singing all the time and creating that buzz."
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