Real Madrid fans were once again disappointed by another uninspired showing from Los Blancos, who spent most of the game behind against Real Sociedad until Vinicius Júnior scored from a rebound in the 89th minute.
La Real's opener came at the 54th minute from a good setup by man of the match Nacho Monreal, who found Cristian Portu on the far right side behind Ferland Mendy's back and headed the ball past Thibaut Courtois.
Earlier in the game Dominican striker Mariano Díaz had missed a sitter for Los Merengues after meeting a cross from Lucas Vázquez, heading toward the crossbar despite the goalkeeper being beaten.
It took a combination of Vázquez and Vinicius, a late substitution, to finally capitalize on Real Sociedad's lazy defending after Real Madrid were wasteful for most of the game, as they now sit five points behind their next opponents, city rivals Atlético Madrid.
The result puts an end to Real Madrid's four win and three clean sheet streak in the worst possible moment, as a trip to the Wanda Metropolitano next Sunday awaits.
Zidane's system change backfires
Los Blancos' worst moment came when manager Zinedine Zidane changed the team setup at the start of the second half, sitting back with Casemiro as centre back, which led to Portu's goal. In the press conference after the game, the Frenchman explained he made that decision as he was dissatisfied with the team's high press in several plays during the first half.