Ole Gunnar Solskjaer’s half-time substitutes proved the difference makers as Paul Pogba took control on his return to Italy.
The midfielder scored the crucial goal just three minutes after coming on.
Pogba’s near post strike was enough to send the red side of Manchester into the quarter-final draw on Friday.
It was the battle of the substitutes at the San Siro as Zlatan Ibrahimovic had a huge chance to level the scoreline but a crucial save from Dean Henderson ensured United booked their place in the last eight.
AC Milan’s team news signalled their intent to defend, no recognised centre forward in the starting line-up for Stefano Pioli’s side.
Manchester United started the game with the midfield of Scott McTominay and Fred, a notorious partnership for Solskjaer in important matches.
The first 45 minutes was fairly uneventful with the sides going into the break at 0-0, which with United’s front three all being on goal droughts and AC Milan without a striker, that hardly came as a surprise.
The hosts got themselves into some positive positions but failed to take advantage of them. Samu Castillejo was presented with their best opening, with Harry Maguire’s last ditch tackle preventing the Spaniard from a potential one-on-one with Henderson.
Similarly, the visitors played some good football at times but couldn’t manage anything more than some shots from distance in the first half. To sum it up in another way, AC Milan acquired an xG of 0.28 and United, 0.14.
Pogba replaced Marcus Rashford at half-time, a change United fans will hope isn’t injury related after the Englishman’s struggles with playing through injury in recent weeks.
For the second time in this tie, Ole Gunnar Solksjaer’s half-time substitutes have made an immediate impact.
With the tie in the balance, a cool head was needed. Pogba provided exactly that after pinball ensued in the Milan penalty area. The Frenchman collected the ball and fired high past Gianluigi Donnarumma to put United 1-0 up on the night and 2-1 on aggregate.
United’s star man has missed 10 games with a thigh injury but displayed the positive qualities that fans attribute to the 28-year-old.
Pogba’s goal ensured control of the tie for the visitors. Milan were struggling to create anything of note when faced with their their imminent exit from the competition which prompted Ibrahimovic’s arrival with 25 minutes left.
Milan’s full-back pairing of Pierre Kalulu and Theo Hernandez were their main threat, with Frank Kessie trying to get provide attacking intent from midfield.
Unlike in the first leg, Henderson was able to make a massive save to deny Milan’s Swedish centre forward from levelling the tie. Milan’s number 11 rose high to get to the ball first but his powerful header was met with an equally strong hand by Henderson.
Despite AC Milan bombarding United in the late stages, like so many others before them, the Rossoneri failed to penetrate the solid United defence and with that came the end of their European campaign.
The overall quality of the two legs may not have lived up to the expectations but three high quality moments defined this tie and that is what European fixtures are all about.