Ronaldo scored his 11th league goal from the penalty spot after substitute goalkeeper Salvador Ichazo had brought down Mario Mandzukic in the box.
Torino has chances themselves, but Armando Izzo headed over and Andrea Belotti had an effort saved.
Juve have collected a possible 46 points from 48 available this term.
The only blemish from their opening 16 games of the season came in a 1-1 draw against Genoa.
Massimiliano Allegri’s side were far from their best against their city rivals, yet managed to grind out victory which extends their lead over second-placed Napoli to 11 points.
They could have had a second goal shortly after breaking the deadlock on 70 minutes, but Croatia striker Mandzukic’s strike at the far post was ruled out for offside by the video assistant referee.