The Basque club's reverse at Getafe's Coliseum stadium in Madrid means they still occupy fourth and Spain's final qualification berth for Europe's elite club competition but their lead over fifth-placed Valencia has been cut to two points after Valencia's 4-0 win at home to Osasuna on Saturday.
San Sebastian-based Sociedad have 58 points with four matches left, Valencia are on 56 and Malaga 53 in sixth. Getafe are eighth on 47 points and still have a chance of securing a place in the Europa League.
"We played really badly but there are always days like this," Sociedad forward Antoine Griezmann said in an interview with Spanish television broadcaster Cuatro.
"We are still two points ahead [of Valencia] and we have a crucial game coming up" [at home to Granada next Monday], the Frenchman added.
Sociedad's golden period came in the 1980s when they twice won La Liga and reached the European Cup semi-finals in 1982/83, where they fell to eventual winners Hamburg SV.
