Gennaro Gattuso's first game in charge of AC Milan ended with Benevento goalkeeper Alberto Brignoli scoring a 95th-minute equaliser to earn the home side their first ever Serie A point.
Milan winger Giacomo Bonaventura opened the scoring for Milan in the first half before the hosts struck back through George Puscas.
Nikola Kalinic then restored Milan's goal advantage with a header, capitalising on the home side's struggle to clear the ball from a corner, but it would be the Benevento goalkeeper who had the final say.
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Deep into the five minutes of stoppage time added onto the end of the game, a free-kick from Danilo Cataldi was met by the head of Brignoli who had been sent into the opposing penalty area to attack the set-piece.
Gianluigi Donnarumma was unable to attempt a save, such was the nature of the header, leaving Benevento to steal a 2-2 draw and record their first point of the season.
"It's such a strong feeling, indescribable," Brignoli told Sky Sport Italia. "I dedicate the goal to all the fans who are living a dream that they hoped would have gone better.
"They [the coaches] told me to go up, that there was nothing to lose. I went to jump, closed my eyes and dived more like a goalkeeper than a striker.
"We've lost so many games unfairly at the end, even against Juventus. For once, after three months of sacrifice by everyone, it's nice to be able to celebrate.
"This draw is for everyone and it would be selfish to talk only about me."
Before Sunday's meeting with Milan at Stadio Ciro Vigorito, Benevento had failed to pick up a single point from 14 league outings and sat firmly at the bottom of the Italian top flight following their promotion from Serie B last season.
Prior to Brignoli's effort, the last goalkeeper to score a goal in Serie A had been Massimo Taibi in Reggina v Udinese, in April 2001.