José Mourinho surprisingly benched Iker Casillas for the game atMálaga, and the move may cost him more than just three points as little-used Adán Garrido was overwhelmed in a 3-2 defeat.
Casillas has been a regular starter for a decade and is the captain of both Real and Spain's world champion national team, and is revered by the club's fans.
Saturday's game was the first time he had not started a meaningful league fixture for the Spanish league champions in 54 matches. Relations between Mourinho and his players were already frayed with the team on the slide, and they are likely to be further strained now. "It surprised us, Iker is our captain," the Real defender Sergio Ramos said.
Mourinho justified the move to omit Casillas by saying that the inexperienced Adán was in better form. "We hadn't been playing well in different aspects of the game, among which was our defence," Mourinho said. "It was a technical decision. My opinion is the one that matters. I analysed the players I had available and picked the team to play. You can invent the story you want but it is a purely technical decision and nothing more."
The defeat was Real's fourth in nine away matches and left the defending champions in third place 16 points behind leaders Barcelona.
Adán had only four previous career starts in the league and had made three starts this season: one in a Champions League game after Real's place in the knockout rounds was already assured and two in Copa del Rey ties against lower-division opponents.
The 25-year-old Real youth product was not tested in the first half as they controlled the ball and the scoring chances. But after half-time he let three shots find his net while making only three saves.
Mourinho defended Adán by saying that he thought the choice of goalkeeper "had no influence in the result". However, Real had not conceded three goals in a league game since a 3-1 defeat by Barça last December, and it was the first time they had conceded three goals to a Spanish league team other than Barça since April, 2011.
The 31-year-old Casillas is respected in Spain and abroad as one of the best keepers in the game. He has been voted the top goalkeeper in the world by players in the FIFPro vote for four straight years and is expected to win again next month.
The last time Casillas did not start a league match was on 5 May last season after Real had clinched the title.
Casillas's mood in the dugout at La Rosaleda stadium went from glum to nervous and finally anguished as he watched his team fail to convert a plethora of chances in the first half, and then get picked apart in the second. At one point he zipped up his sweatshirt to hide half his face.
The Málaga forward Isco shot past Adán to open the scoring before Joaquin Sánchez set up Roque Santa Cruz to score twice more.
Málaga's goals were well taken, but if doubts were already brewing about Mourinho's ability to continue at the helm of Real, then his critics received a big boost.
Mourinho scoffed at the question of whether he feared for his job heading into the winter break with little hope of retaining the title.
"Fear for my job?" he said. "I have never feared for my job."
But in the next breath he acknowledged that "football has no memory. The only thing that matter is the present, not the titles you have won".