The Old Lady showed some good combination play in the early satges of the first half, although clear-cut chances were hard to come by in the opening 15 minutes.
The hosts went agonsingly close in the 38th minute when Sassuolo shot-stopper Andrea Consigli pulled off a stunning save to stop Pol Lirola from deflecting the ball into his own net.
Sassuolo did see a bit more of the ball as the half drew to a close, but the score remained goalless as the sides entered the halftime break.
It was Ronaldo who got the breakthroug goal in the 50th minute as a poor clearance landed at the feet of the Portuguese, who had the simple tasking slotting into an empty net.
It was proving to be Ronaldo's day as the forward completed his brace on 65 minutes with a left-footed striker after being picked out by Emre Can.
Chances continued to fall for Juventus and Ronaldo as the half went on, but the Portuguese failed to capitalise with a couple glaring misses after 80 minutes.
The visitors set up a nervous final few minutes when Khouma Babacar nodded home from close range, while Douglas Costa was sent off for an off-the-ball incident.
However, Juve held on to claim three points and their fourth win of the season.