Barcelona were denied a chance to surge to the top of the La Liga table as Real Sociedad didn't allow Luis Enrique's men to score after Spaniard Jordi Alba's early own goal.
Real Madrid's 2-1 defeat at Valencia earlier in the day would have allowed Barca to edge ahead in the title race if they had won, but Enrique started with Lionel Messi, Neymar and Dani Alves on the bench following the festive break.
And they were unable to inspire a fightback as David Moyes secured a memorable second win as Sociedad manager, the BBC reported.
Messi, Neymar and Alves only returned to training last Friday after an extended break in South America during the league's Christmas shutdown and Enrique took the gamble of starting without them for a fixture that has proved tricky for Barca in the past.
And so it proved again with their winless run at Anoeta now extended to six games.
In Moyes' previous two home La Liga games, former Arsenal striker Carlos Vela had struck in the opening five minutes.
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And although there was to be no repeat for Vela, Sociedad still took the lead after just two minutes as Alba headed a cross from Sergio Canales past his own keeper.
Sociedad have been difficult to beat under Moyes, with just two losses in their previous seven matches since the former Manchester United and Everton boss took over in November, and they clung tenaciously to their lead, the report added.