Even though their twogoal lead was intact, the Nerazzurri were still dealt a blow before the break, as Mkhitaryan was forced off injured.
In a city revered for fashion, it was Inters grit and organisation that kept Milan out, giving Martnez the platform to smash a shot past Maignans outstretched hand to put Inter ahead on the night and take the tie out of sight for Milan.
Emotions ran high after that moment, as Inter booked their tickets to the UCL final in Istanbul with their ninth match unbeaten across all competitions.
While the Nerazzurri wait to see whether they will face Manchester City or Real Madrid in June, Milan will be praying that they can find a way into Europes premier club competition for next season after winning one of their last five, as they currently sit four points behind the fourth and final UCL qualification spot in Serie A.
They confirmed their journey to Istanbul with a 30 aggregate victory against their Milan neighbours, winning a fourth consecutive Derby della Madonnina without conceding.
Despite the San Siro being predominantly filled with Nerazzurri shirts, it was Milan who got off to the better start on this occasion.
Tho Hernandez came agonisingly close with an audacious strike, but Brahim Daz didnt show enough conviction to beat Andr Onana after brilliant work from Sandro Tonali to tee him up, as Stefano Piolis side pursued the goal they so desperately needed.
Inter stood firm against the Rossoneri blitz and started to threaten with their own forays forward, although Henrikh Mkhitaryan fired over from Edin Dekos cutback.
With the two teams going toetotoe, Rafael Leo came tantalisingly close to marking his return from injury with the most vital of goals as the winger raced behind Matteo Darmian but eventually dragged his shot agonisingly wide, before Dekos header brought an incredible save out of Mike Maignan and Lautaro Martnez soon struck off target.
Inter Milan are through to the final of the 2023 UEFA Champions League after piping AC Milan 10 in the second leg of the semifinals on Tuesday night.
It is Inters first return to Champions League finals since their 2010 triumph.