Cristiano Ronaldo scored his first two goals for Juventus as the Italian champions maintained their perfect start to the season.
The forward, goalless in his first three games since his summer move from Real Madrid, tapped in from inside the six-yard box 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 but Juve held on.
Ronaldo has scored a total of 400 league goals in 517 matches during the course of his club career (Juventus, Real Madrid, Manchester United, Sporting CP).