Milan ended Alessandria's fairytale, winning 5-0 to ease into the Coppa Italia final.
Two goals each from Jeremy Menez and Alessio Romagnoli and a last-gasp Mario Balotelli strike saw the Rossoneri advance 6-0 on aggregate.
The Lega Pro visitors were trailing 1-0 after the semi-final first leg, but still brought almost 15,000 fans to San Siro.
The third-tier side weren’t simply looking to frustrate, but should have been behind with seven minutes played.
Juraj Kucka broke into the box, and unselfishly cut the ball back for Keisuke Honda, who had taken up a position 12 yards out.
The goal was gaping, but somehow the Japanese international contrived to fire it over when it seemed easier to score.
The Grigi could have taken the lead at the other end just moments later, but Abbiati came out for a smart save after his own poor distribution had presented Simone Iocolano with a chance.
The deadlock was broken with 18 minutes played. Honda lifted a ball over the top for Menez, and the Frenchman controlled the ball on his chest before firing a fantastic finish across Gianmarco Vanucchi.
It was 2-0 soon after, when Giacomo Bonaventura’s corner was headed down by Kucka and Alessia Romagnoli turned it in on the half-volley.
The Alessandria defenders appealed for an offside, but replays confirmed the young centre-back was being played on.
Sinisa Mihajlovic’s side put the game and the tie to bed with seven minutes until half-time. Andrea Poli cut the ball back for Menez, who made no mistake ingetting his second of the game.
The Rossoneri appeared to take their foot off the gas at the beginning of the second half, knocking the ball around comfortably but without really threatening the goal.
Despite Mihajlovic demanding a performance from Balotelli before the match, the striker was a peripheral figure.
With 20 minutes remaining the on-loan Liverpool striker sent a free-kick sailing over the bar, drawing whistles from the San Siro crowd.
The Lega Pro side must have known the tie was over, but were still seeking a famous goal at San Siro, and Mattia De Sciglio cleared an effort off the line on 76 minutes.
Instead it was the Diavolo who inflicted further misery. Romagnoli once again got on the end of a corner, and the goal-line technology revealed his effort had crossed the line.
Despite attracting the derision of the fans earlier in the match, Balotelli made it five with virtually the last kick of the game.
The striker beat the offside trap, and slotted the ball through Vanucchi's legs with his customary cool.
The Rossoneri will now face either Juventus or Inter in the final, with the Bianconeri holding a 3-0 lead after the first leg.
Milan 5-0 Alessandria (6-0 on aggregate)
Menez 20 39 (M) Romagnoli 24 81 (M) Balotelli 90 (M)
Milan: Abbiati; De Sciglio, Zapata, Romagnoli, Antonelli; Honda, Poli, Kucka (Mauri, 45), Bonaventura (Boateng, 58); Balotelli, Menez (Bacca, 74)
Alessandria: Vannucchi; Celjak, Morero, Sirri, Sabato; Nicco, Loviso (Mezavilla, 71), Branca (Bocalon, 83); Marras, Fischnaller, Iocolano (Marconi, 62)