The score says how it ended. xG says how it should have ended: it is the sum of the chances each shot was worth, not an opinion about the game.
Atalanta won against the run of chances: Sassuolo created more (2.70 xG against 0.92).
Atalanta: +3.3 for the season (11 in the table). Sassuolo: −0.6 (10). The gap between points and xPTS is built from matches like this one.