Miralem Pjanic's delightful finish from 25 yards put the Italian champions ahead before Mario Mandzukic struck from close range after half-time.
Ronaldo, a £99.2m summer signing from Real Madrid, has not scored in two Serie A games.
Sami Khedira hit a post for Juve when the game was goalless.
Fans held up banners and posters supporting Portugal forward Ronaldo, making his first competitive appearance for Juve at the Allianz Stadium.
However, he touched the ball only once in the Lazio penalty area in the first half and, shortly before Juve's second goal, had a dipping shot superbly tipped over by Thomas Strakosha.
Ronaldo also missed inside the six-yard box, Joao Cancelo's low cross hitting his heel only to rebound to Mandzukic, who doubled Juve's lead.
Juve have six points from two games, Lazio have lost both their opening games.