The hosts, who were winless in the previous seven meetings, had the first chance of note when Brooke Norton-Cuffy burst past his man and into the box, only for Mike Maignan to pounce low to his right and tip the resulting shot to safety.
The goalkeeper was on hand again shortly afterwards to make an even better stop from Junior Messias, whose stabbed effort from point-blank range was heading into the bottom corner.
Sergio Conceicao’s side eventually grew into proceedings, and they finally tested Nicola Leali in the 38th minute when Theo Hernandez saw a speculative 25-yard strike saved.
Moments later, Stefano Sabelli’s swinging effort was kept out the other end, before the Genoa goalkeeper was called upon for a second time, this time superbly dashing off his line to block Christian Pulisic’s drive and ensure the two teams went to the break all square.
Driving rain at the Stadio Luigi Ferraris was making things more and more difficult as the match proceeded, with players from both sides struggling to stay on their feet. Chances still flowed though, as Hernandez had a long-range free-kick saved.
Patrick Vieira’s side then saw Frendrup whip the wrong side of the post, before substitute Vitinha, who had only been on the field for a matter of seconds, scored with his first touch, ending a year-long drought by converting with a delicate volley from a delicious Aaron Martin cross.
Milan, who have picked up the joint-second most number of points from losing positions in Serie A this season, and they duly did through their own substitute, Rafael Leao, who saw a deflected strike from near the penalty spot balloon past Leali.
Seconds later, the comeback was complete, as Frendrup inadvertently smuggled a cross into his own net, shattering Genoa hearts in the process.
Indeed, they struggled to find any real response and ultimately slipped to a third successive defeat that damages their hopes of ending a ten-year wait for a top-half finish in Serie A, whereas their visitors have won three away games in a row for the first time since March 2024.
Flashscore Man of the Match: Theo Hernandez (AC Milan)