La Liga leaders Barcelona wasted a huge chance to extend their lead at the top as they were surprisingly beaten by lowly Almeria.
With second-placed Real Madrid drawing on Saturday, Barca knew a win on Sunday would take them 10 points clear.
But El Bilal Toure's superb first-half strike settled the game to boost Almeria's hopes of avoiding relegation.
It is Barca's second big loss this week following Thursday's Europa League exit at the hands of Manchester United.
Prior to that 3-2 defeat in Manchester, they had gone unbeaten in 18 matches in all competitions.
The loss to Almeria ends a seven-game winning streak in La Liga for Xavi's side.
The home side should have won by more but Leo Baptistao's strike was blocked by goalkeeper Marc-Andre ter Stegen.
Rodrigo Ely then missed a sitter from close-range, sending wide a header from a corner when he was all alone in the area.
"I'm very angry because I think we made the worst game of the season by far, mainly in the first half," Barca boss Xavi told Movistar Plus.
"We were not good and wasted a great opportunity in a match we could not afford to lose after what happened to Real Madrid.
"It was a golden opportunity today and it ended with a really bad day for us. No excuses, it was the worst showing of our side in the entire season."
