Three first half goals gave Osasuna victory over Atletico Madrid as Los Colchoneros fell off the pace at the top.
Barcelona’s defeat to Real Sociedad meant Atletico could have pulled away from the Catalans and gone level with Real Madrid - Atleti’s next opponents.
Instead Real Madrid are alone at the top of La Liga, three points clear of Barca and Atletico.
Diego Simeone named a much-changed side, picking Diego Costa, David Villa and Adrian in something approaching a 4-3-3 formation.
Osasuna Coach Javi Gracia named the same XI as drew 0-0 at Elche, looking to continue the upswing in form that had brought four points from their last two games.
Simeone went without Raul Garcia, Koke and Arda Turan but Atleti struggled to impose themselves on the game as Simeone’s attempt to protect his side prior to the Madrid derby backfired.
Osasuna took a commanding and fully-deserved three-goal lead by half-time, Alejandro Cujedo, Emiliano Armenteros and Roberto Torres all netting before the interval.
Cejudo’s opener came a well-worked set-piece, Osasuna taking a short corner and the men in the penalty area dragging the Atleti markers to the near post as the ball sailed over them, to be met by a completely unmarked Cejudo.
Armenteros, deliverer for Cejudo, then capitalised on some lax defending from Juanfran to hit a rasping drive off the post and past Thibaut Courtois.
Torres added a third with five minutes of the half to go and it wasn’t a score line to flatter the hosts.
Osasuna, with only four wins at home prior to kick-off, had taken points off Barcelona and Real Madrid earlier this season and Atletico were soon finding out why. Crosses rained into the Atleti area and the pace and trajectory of the delivery caused problems.
Atletico made only sporadic incursions into the Osasuna half in the opening 45 minutes and the title challengers failed to create a chance of note, Diego Costa going closest with an effort from the edge of the area that swerved wide.
Koke was introduced at half-time in place of the carded Mario Suarez while Osasuna made a change too, Oier coming on for the injured Marc Bertran.
The substitutions were the only thing of note in the opening 10 minutes of the second half as Atletico tried without success to get back into the tie. Osasuna were able to repel the Atletico attacks with a well-organised defence.
Diego Costa resorted to flopping to the turf in an attempt to win a penalty, but you’ll go a long way to see a more blatant dive this season.
It was especially risky as Costa went into the game one yellow card away from a suspension and if the referee had been on the ball, the forward would miss Madrid’s return to Vicente Calderon next week.
Garcia nearly pulled a goal back with 13 minutes to play when he connected with Koke’s cross but the ex-Osasuna midfielder couldn’t hook the ball into the far corner.
Juanfran was the next to try but Andres Fernandez batted the ball away, the goalkeeper’s first real save of the game.
Atletico had further sights on goal - with Costa blasting over - but it was too little, too late. Osasuna moved three points further away from the drop zone and Atletico’s title push suffered what could be a terminal blow.
Osasuna 3-0 Atletico
Scorers: Cejudo 6, Armenteros 20, Torres 41
Osasuna: Fernandez, Bertran (Oier 46), Loties (Flano 80), Arribas, Damia; Lolo, Silva; Cejudo (Loe 84), Armenteros, Roberto Torres; Riera
Atletico: Courtois, Juanfran, Alderweireld, Godin, Filipe Luis; Mario Suarez (Koke 46), Gabi, Diego (Turan 49), Adrian; Diego Costa, Villa (Garcia 61)