Visitors remain in bottom three after defeat
After a slow opening, it was Joseba Llorente who gave the home side the lead after 16 minutes, when he was the recipient of a pinpoint Alberto De le Bella cross and headed the ball past 'keeper Daniel Aranzubia.
Deportivo's only real chance of the first half came from Yves Desmarets, whose shot flashed just wide of the post.
Real Sociedad goalkeeper Claudio Bravo was called into action early in the second half, when he had to make point-blank saves from Riki and Adrian, but it was the home side again who found the back of the net with 20 minutes to go thanks to Antoine Griezmann.
The striker followed up on Xabi Prieto's knock-down and made it 2-0.
Imanol Agirretxe rounded off the scoring in the 85th minute, when he got on the end of a measured pass from Jeffrey Saprong and poked the ball home.
The win lifts Sociedad out of the drop zone, condemning Deportivo to 19th place in the Primera Division.