League leaders Barcelona suffered only their second La Liga loss of the season, falling to Real Sociedad with teenage sensation Lamine Yamal sidelined due to injury.
The defeat leaves Barcelona six points clear at the top of the table, though second-placed Real Madrid holds a game in hand.
Sheraldo Becker’s first-half goal proved decisive for the hosts, who fully deserved the win and missed multiple opportunities to extend their lead.
Robert Lewandowski saw a first-half goal controversially ruled offside for Barcelona, who struggled in both attack and defense throughout the match.
Despite Barcelona’s prior four-game winning streak in San Sebastian, they appeared uninspired offensively and vulnerable at the back.
The substitution of Dani Olmo for an ineffective Frenkie de Jong had little impact, and without 17-year-old Spain international Yamal—who was injured in the Champions League match against Red Star Belgrade—the visitors failed to register a single shot on target.