Barcelona’s Anoeta Stadium jinx struck again when they lost 1-0 at Real Sociedad on Saturday, their second successive defeat in La Liga.
Elsewhere, Cristiano Ronaldo became the first player to hit 30 La Liga goals in six consecutive seasons as he inspired Real Madrid to a 4-0 thrashing of Eibar while Fernando Torres was on target as Atlético Madrid won 3-1 at Espanyol.
The winger Mikel Oyarzabal headed the only goal for Sociedad in the fifth minute against Barça, who were without their top scorer Luis Suárez through suspension and fielded a much-changed side and managed only five shots on target.
Luis Enrique’s side have 76 points with six games to go, three ahead of Atlético and four in front of Real Madrid.
After going unbeaten in all competitions for six months, Barcelona followed last week’s 2-1 defeat by Real Madrid with another slip-up. The European champions are without a victory in three league games, their longest stretch since Luis Enrique took charge in 2014.
The coach made four changes to the team that lost to Real Madrid, bringing back the midfielder Rafinha after a six-month injury absence and starting without Andrés Iniesta, Jordi Alba and Ivan Rakitic.
Barça were handed their fifth defeat in six visits to Sociedad after the 18-year-old Oyarzabal nodded in a cross from Xabi Prieto.
The visitors struggled to get back in the game and the Sociedad goalkeeper Gerónimo Rulli did well to save from Lionel Messi twice, substitute Iniesta and Arda Turan.