Barca, who can restore their eight-point advantage with a victory at Rayo Vallecano on Thursday, have 66 points from 26 games, while Atletico have played a game more.
Third-place Real Madrid, who play at Levante on Wednesday, have 54 points, while Sociedad are ninth with 34.
Atletico took the lead after eight minutes when Sociedad midfielder Diego Reyes scored an own goal trying to cut out a cross from Keko.
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Diego Simeone’s side went further in front a minute into the second half when striker Luciano Vietto latched onto a poor clearance and pulled the ball back for Saul Niguez to shoot past Geronimo Rulli.
Atletico completed their biggest home win in the league this season when Antoine Griezmann converted a 61st-minute penalty against his former club, after the Frenchman had been brought down by Alberto de la Bella.
The visitors came closest to pulling one back when Jonathas headed against the post two minutes later after being set up by Ruben Pardo.
Atletico defender Diego Godin, Griezmann and Vietto all missed other chances in a one-sided first half.
(Writing by Rex Gowar; editing by Toby Davis)
