Cristiano Ronaldo scored his first two goals for Juventus as the Italian champions maintained their perfect start to the season.
Ronaldo, goalless in his first three games since his move from Real Madrid, tapped in shortly after half-time.
The 33-year-old then finished off a rapid counter-attack by shooting into the bottom corner after 65 minutes.
Sassuolo pulled one back in added time via Khouma Babacar and Douglas Costa was sent off but the hosts held on.
Juve's Brazilian winger was dismissed after a video assistant referee intervention for spitting at Federico di Francesco.
Ronaldo could have completed a hat-trick late on but missed two easy chances from inside the penalty area.
The win is Juventus' fourth from four games this season.