The 19-year-old forward, on loan from Juventus, netted a 26-minute hat-trick in the first half and was on target again just after the restart as Sassuolo battled from 2-0 down to haul themselves out of the Serie A relegation zone.
Robinho and Mario Balotelli scored for Milan before Berardi's glut of goals, with Riccardo Montolivio pulling one back late on.
It was a performance that will live long in the memory of Sassuolo fans as well as Berardi, who now has two hat-tricks to his name this season and is the only player to score four goals in one game against Milan.
"It is an evening I will certainly never forget," he told Sky Sport Italia.
"I am happy for the four goals, but above all because this was an important win for Sassuolo and we really needed that boost."
The teenager dedicated his four-goal haul to a number of people after the game, including his coach, girlfriend, and team-mate Francesco Acerbi, who has recently undergone treatment for testicular cancer.
Berardi also went on to give his backing to head coach Eusebio Di Francesco, adding: "It has been a tough time this week with rumours about whether the coach would leave or not, so this win may well be decisive for his time here.
"We're glad to keep him, as he took us into Serie A and has a huge heart, just like the players."
And Berardi admitted he found himself a little star-struck by Milan's formidable line-up, most notably by Brazilian playmaker Kaka.
He added: "I asked Kaka for his jersey, as my friend wanted it.
"He's a great champion and I’m happy to have it even for a little while."
