Carlos Vela's 10th-minute effort at the Estadio La Rosaleda was enough for Jagoba Arrasate's men against struggling Malaga.
With Sevilla and Valencia playing out a 0-0 draw in the 24th round, Sociedad are eight points clear in sixth.
Espanyol and Levante are locked on 32 points with Sevilla and Valencia, but all four teams have a lot of work to do if they are to finish in one of the two UEFA Europa League places.
Malaga are still dangerously close to the relegation zone, just three points clear of 18th-placed Real Valladolid.
Vela was on the end of a fine team move which led to the game's only goal on 10 minutes.
Antoine Griezmann flicked a pass over his marker and onto the overlapping run of Jose Angel Valdes, whose cutback found the run of Vela on the penalty spot.
The Mexico international did the rest, neatly finishing into the bottom corner to give his side a 1-0 lead.
Sociedad still have hope of playing in next season's Champions League, sitting four points behind fourth-placed Athletic Bilbao.
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