Juve conceded a last-gasp goal to Lazio last time out to make it only three wins from seven league outings this term, but Ronaldo inspired them to three points on Saturday by scoring for the fifth league game running.
Federico Bernardeschi had an early goal ruled offside before Ronaldo struck twice in a four-minute spell before the break.
He will be especially eager to secure Champions League glory with Juventus - Andrea Pirlo's side are now second in Group G with six points from three games.
Lazio also won 2-0 under torrential rain at Crotone, but Atalanta were held 0-0 at promoted Spezia days before their Champions League trip to Liverpool.
Juventus coach Andrea Pirlo says the time for excuses is over.
The Portuguese striker blasted in an Alvaro Morata cross after 38 minutes, latching onto a Merih Demiral nodded cross off a corner for the second from close range minutes later.
Atalanta are sixth, level on points with seventh-placed Lazio after eight games.
Ciro Immobile marked his recovery from the coronavirus with a goal to send Lazio on its way to victory at last-place Crotone.
Atalanta and Spezia both struggled in a match of few chances.
Atalanta also hit the woodwork at the end of the first half through Duvan Zapata.
It was Immobile's first match in almost three weeks after being ruled out with COVID-19, which also kept him out of Italy's three matches.
The visitors nearly won the match late on but Spezia goalkeeper Ivan Provedel pulled off a stunning double save to deny first Mario Pasalic and then Robin Gosens. Crotone remained bottom with just two points from its opening eight matches.