Diego Simeone and Atletico Madrid were dealt a hammer blow on Sunday night as they fell to a 2-1 defeat against Athletic Club at San Mames.
The result has blown the title race wide open, with Atletico able to drop from top spot for the first time in 19 games if Barcelona win their game in hand against Granada on Thursday evening.
The LaLiga Santander leaders faced a weakened Athletic side as Marcelino opted to make changes, but the youngsters in the team started with an intensity that wasn’t matched by the line-up chosen by Simeone, who opted for just one change from the 2-0 win over Huesca in midweek.
Alex Berenguer converted the opening goal eight minutes in after a rapid counter-attack caught Atletico out, with a lacklustre start from Los Colchoneros leaving the team frustrated.
Simeone did react, bringing on Luis Suarez, Joao Felix and Thomas Lemar just shy of the hour mark as the trio all made their return from injury, but it was not enough to win the game.
Stefan Savic rose highest to level the scores in the 77th minute with a header from a corner, but it was another corner which would break Atletico hearts.
With just four minutes left on the clock, Inigo Martinez headed into the Atletico net, beating Jan Oblak.
Atletico could therefore lose their position as leaders of LaLiga Santander on Thursday, but, assuming Barcelona pick up maximum points against Granada and Valencia, they could wrestle back top spot when they travel to the Camp Nou on Matchday 35.
It means that Atletico could drop from first position for the first time since mid-December, while Barcelona could become leaders for the first time this season.
Barcelona now face Granada, Valencia, Atletico, Levante, Celta Vigo and Eibar, while Atletico will be hoping to avoid any more slip-ups against Elche, Barcelona, Real Sociedad, Osasuna and Real Valladolid.
Sunday’s draw means a major blow for Simeone and his players, having led by as many as seven points in January, at which point they seemed nailed on to win the title. Now, they cannot afford any more mistakes.