Ronaldo's first and Madrid's second saw him achieve the landmark in only his 92nd game.
Gonzalo Higuain opened the scoring before further first-half strikes from Ronaldo and Karim Benzema seemed to put the result beyond doubt.
Xabi Prieto immediately pulled one back, but after the interval Benzema and Ronaldo completed their braces and Madrid strolled to the victory.
It took Madrid, decimated by events at Villarreal in midweek, only six minutes to opening the scoring. Benzema passed inside to Higuain and the Argentina striker swept a lovely finish past Claudio Bravo from 18 yards.
Real Sociedad were woeful, lacking ambition and showcasing a three-at-the-back system that they attempted to use in conjunction with the offside trap.
It backfired as Madrid tore them apart down the flanks. Indeed, the away side were fortunate not to concede more goals as the linesmen flagged Ronaldo and co offside several times when they looked level.
Imanol Agirretxe was put in by chance following a mistimed Asier Illarramendi shot but, as was often the case for the visitors on the night, he dithered and Iker Casillas was able to make a save.
Ronaldo was denied by Bravo after exchanging passes with Higuain to race through on the left then the Portuguese missed a glorious chance inside the six-yard box, glancing his free header wide of the post.
On 32 minutes he had his 100th goal, springing the offside trap to curl home inside the far post.
Xabi Alonso sent a supreme long ball from his own half for Benzema to control and lob Bravo on 40 minutes, but barely a minute later Prieto bent a superb strike into the far top corner via the head of Sergio Ramos.
Madrid were missing Pepe and Mesut Ozil as well as Jose Mourinho and assistant Rui Faria from the touchline after the controversial midweek draw, although a technicality allowed Ramos to play despite also seeing red in that match for two bookings.
Four minutes into the second period Benzema lifted a lovely finish past Bravo after Sami Khedira's astute first-time pass for 4-1 to soothe any nerves and seven minutes further on Ronaldo completed the scoring, Higuain sending a perfect low cross from the right for the Portuguese to finish Liga goal number 101 from just outside the six-yard box.
Xabi Alonso was extremely lucky to escape a second yellow card after standing on Prieto's foot after the ball had gone.
Turk Nuri Sahin made only his second appearance for Real this season after leading Borussia Dortmund to the Bundesliga title in the last campaign, while Jese came on for Ronaldo to make his Liga debut.
The third sub, Fabio Coentrao, should have scored a sixth goal from a Ronaldo cross before the superstar was withdrawn nine minutes from time.