Atalanta will be playing in the Champions League next season after securing a top four finish on the final day of the season.
After a strong finish to the campaign, which included a recent draw away to league champions Juventus, Atalanta came from behind to defeat Sassuolo and take a European spot at the expense of giants AC Milan.
Domenico Berardi scored early for the visitors, but Atalanta kept focused and were handed the advantage after Berardi went from hero to villain and got himself sent off.
Goals from Duvan Zapata, Alejandro Dario Gomez and Mario Pasalic helped turn the tie on its head, as Sassuolo faded late on.
Francesco Magnanelli was also given his marching orders, as the away team finished the match with nine men.
It was a dramatic final day flourish to Serie A, with both Milan sides uncertain of their European standing.