Real Madrid could be stripped of their current label as the champions of Spain by the end of next week after falling to defeat at Real Sociedad.
The ten men of Los Blancos were poor throughout in the Basque country and now sit 14 points behind La Liga leaders Barcelona with only five games to go.
They could also be overtaken by city rivals Atletico Madrid should they win their game in hand.
La Reale were on course for a deserved win even both sides had 11 men on the pitch and are in a great position to qualify for next season's Champions League.
Real Madrid came close to taking the lead early on through an unlikely source, with Aurelien Tchouameni forcing a fine save out of Alex Remiro with a stinging strike from distance.
Remiro was called into action again soon after to tip a thumping header from Eder Militao over the crossbar.
Down the other end, Alexander Sorloth saw a strike deflected narrowly over following a great last-ditch block by Militao.
Real Sociedad went close again when Mikel Oyarzabal teed up David Silva, but the former Manchester City star was leaning back and so skied a shot from close range.
Within the next minute, the hosts should have led. Sorloth flicked a corner on at the near post and from two yards out, Martin Zubimendi directed the ball up and onto the crossbar rather than into the net.
Silva went close again during a manic opening 20 minutes, this time being kept out by the boot of Thibaut Courtois from around 12 yards out.
Though Real Madrid took the sting out of the game for the rest of the first half, they were undone by an error at the start of the second. Militao was pressed into an error by Sorloth and tried to play the ball back to Courtois, but it was wayward and former Madrid youngster Take Kubo was on hand to tap into an empty net.
The visitors' night went from bad to worse after Dani Carvajal was shown a second yellow card after a rash challenge on Aihen Munoz.
Courtois had to be alert to palm away a massively-deflected free-kick from 20 yards as Real Sociedad went for the kill late on.
And that late clincher came with five minutes remaining. Silva won the ball back in midfield and picked out substitute Ander Barrentxea with a magnificent switch of play, with the winger cutting inside and firing in at the near post.
In stoppage time, Remiro spilled the ball but Real Madrid could not capitalise amid a scramble in the hosts' box as the visitors' misery was compounded.
Barcelona will clinch La Liga with a win at rivals Espanyol this weekend, though Real Madrid at least have a chance to claim some silverware in the Copa del Rey final against Osasuna on Saturday.
Real Sociedad player ratings (4-3-3)
GK: Alex Remiro (7); RB: Andoni Gorosabel (6), CB: Igor Zubeldia (7), CB: Robin Le Normand (7), LB: Aihen Munoz (6); DM: Martin Zubimendi (7), CM: Mikel Merino (7), CM: David Silva (9); RW: Take Kubo (9), CF: Alexander Sorloth (7), LW: Mikel Oyarzabal (6)
SUBS: Aritz Elustondo (6), Jon Pacheco (6), Ander Barrentxea (8), Carlos Fernandez (N/A), Asier Illarramendi (N/A)
Real Madrid player ratings (4-3-3)
GK: Thibaut Courtois - 6/10 - Made some decent saves both when drawing and behind.
RB: Dani Carvajal - 1/10 - Picked up a dumb booking for dissent. Picked up a dumber one for a bad tackle.
CB: Eder Militao - 2/10 - Was Real Madrid's best defender until unforgivably giving the ball away so cheaply for the opener.
CB: Antonio Rudiger - 4/10 - Unable to deal with the swarm of Real Sociedad.
LB: Nacho Fernandez - 3/10 - Running in quicksand against the tricky Kubo.
DM: Aurelien Tchouameni - 4/10 - Didn't do an amazing job of controlling the pace of the game.
CM: Dani Ceballos - 3/10 - It was hard to notice that Ceballos was even playing.
CM: Toni Kroos - 4/10 - Played some decent passes but this was not the game for an immobile midfielder.
RW: Marco Asensio - 4/10 - Lacked the creativity and ingenuity that he has shown in recent weeks.
CF: Mariano Diaz - 2/10 - Don't be shocked if this was the last time we saw the invisible Mariano in a Real Madrid shirt.
LW: Rodrygo - 5/10 - Showed glimpses of promise but nothing sustainable to carry a poor Real Madrid side.
Substitutes
Alvaro Rodriguez (59' for Mariano) - 4/10
Lucas Vazquez (63' for Kroos) - 5/10
Sergio Arribas (82' for Asensio) - N/A
Manager
Carlo Ancelotti - 3/10 - Made the understandable call to rest key men ahead of the Copa del Rey final and Champions League semi-finals, but goodness me was this a pathetic showing.
