Nineteen-year-old forward Domenico Berardi scored four quickfire goals to give Sassuolo a 4-3 win over AC Milan on Sunday after they overturned an early two-goal deficit against the seven-times European champions.
Berardi became the first player in Serie A's 85-year history to score four goals against Milan in a league match as he wrote another chapter in their miserable season.
Milan's defeat, against a team who had not scored in their previous five league games, left them languishing in 12th place in Serie A, which ultimately saw their coach Massimiliano Allegri's sacked.
Berardi, a lanky striker with a fiery temper, had not even played organised football until he was 16. His fortunes changed when he visited his brother at university, took part in a match and was pointed out to a Sassuolo youth-team coach.
Having turned professional in 2012, he helped Sassuolo out of Serie B last season as they reached the top flight for the first time, and was bought by Juventus who then loaned him back.
Milan, who have won only five league games all season, looked to be cruising after Robinho and Mario Balotelli put them two goals ahead after 13 minutes.
Berardi began Sassuolo's fightback in the 15th minute when he rounded Christian Abbiati to score from a narrow angle. He levelled with a clever half-volley in the 28th minute and completed his hat-trick just before the break when he got between two defenders to fire past Abbiati.
Straight after the re-start, Berardi struck again with a deflected shot to become the first player to score four goals against Milan in Serie A.
Milan dominated the final half hour and Japan midfielder Keisuke Honda hit the crossbar after coming on in the second half for his debut.
They hit the woodwork three times, repeatedly appealed for penalties and pulled one goal back through Riccardo Montolivo, but they could not force an equaliser despite five minutes of stoppage time.
Meanwhile, Juventus, Roma and Napoli hit 11 goals between them to deliver a blow to pursuers Fiorentina and Verona in the other matches of the night.
Juventus had been looking for a club record of 11 successive wins and despite conceding a 21st minute opener to Mauricio Pinilla the champions fought back in clinical fashion with Fernando Llorente netting twice in a 4-1 win at Cagliari.
Roma began the day eight points behind leaders Juve but had little trouble dispatching Genoa, who were reduced to 10 men before the hour, 4-0.
Alessandro Florenzi led the rout with a sublime overhead kick, with further goals coming courtesy of club captain Francesco Totti, Maicon and Mehdi Benatia.
Napoli were two points further adrift but despite a potentially tricky fixture returned from high-flying Verona with a precious 3-0 win.
Torino 0 Fiorentina 0
Atalanta 2 (Denis 67-pen, Moralez 86) Catania 1 (Leto 89)
Cagliari 1 (Pinilla 21) Juventus 4 (Llorente 31, 76, Marchisio 73, Lichsteiner 80)
Verona 0 Napoli 3 (Mertens 27, Insigne 72, Dzemaili 76)
Roma 4 (Florenzi 25, Totti 30, Maicon 43,
Benatia 52) Genoa 0
Sassuolo 4 (Berardi 15, 28, 41, 47) AC Milan 3 (Robinho 9, Balotelli 13, Montolivo 86)