Atletico Madrid's top-four hopes suffered another blow as they crashed to a disappointing 2-0 defeat at the hands of Athletic Bilbao.
Athletic Club deservedly took the lead after just eight minutes even if the opener came in fortuitous circumstances, with Inaki Williams' shot taking a wicked deflection off Mario Hermoso to leave Jan Oblak with no chance.
The visitors looked disjointed in the early stages and almost fell further behind, with Inaki Williams agonisingly close to getting on the scoresheet when his wicked cross cannoned off the post.
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Diego Simeone changed the system in response to his side's desperately poor start, moving to a back four, as Atleti grew into the contest. Antoine Griezmann registered their first shot on target in the 43rd minute - a tame header - and Yannick Carrasco went close following a lung-busting run.
After the restart, Griezmann's search for a first league goal since November was almost ended with a terrific free-kick that rattled the crossbar.
But Atleti soon had a mountain to climb when Renan Lodi's lax pass was intercepted by Iker Muniain, who drew the foul from Hector Herrera and Inaki Williams coolly dispatched a Panenka penalty past Oblak.
Desperately chasing the game, Atleti threw players forward in search of an unlikely comeback, but it was the home side that looked most likely to grabbing the third goal on the counter-attack.
The result leaves Atletico Madrid four points above fifth-placed Real Betis having played a game more, while eighth-placed Bilbao moved to within a point of a Europa Conference League spot.
TALKING POINT - A day to forget for Los Colchoneros
Atletico Madrid's weak defence of their title was underlined earlier in the day as rivals Real Madrid were confirmed as champions with four games to spare, but Diego Simeone's side have much more pressing matters to deal with - most notably, their place in next season's Champions League.
Atleti have a difficult run-in, starting next week with the visit of the newly-crowned champions, and with rivals Real Betis and Real Socieded still to face, their destiny ultimately lies in their own hands. However, judging by this performance and those of late, they have very right to be worried about slipping out of the top four.
Athletic Bilbao: Simon 7, De Marcos 7, Alvarez 7, Martinez 7, Yuri 7, N Williams 7, D Garcia 6, Vesga 6, Iker Muniain 7, I Williams 8*, R Garcia 7.. subs: Berenguer N/A, Vencedor N/A, Zarraga N/A, Balenziaga N/A, Vivian N/A.
Atletico Madrid: Oblak 6, Llorente 5, Gimenez 5, Hermoso 5, Reinildo 5, Carrasco 6, Herrera 5, Kondogbia 5, Lodi 4, Suarez 5, Griezmann 5.. subs: Koke 5, Correa 5, de Paul 5, Vrsaljko 5, Cunha 5.
8' - GOAL! ATHLETIC BILBAO 1-0 ATLETICO MADRID (HERMOSO OWN GOAL): This has been coming! Inaki Williams brushes off Gimenez as he closes in on goal from the left of the penalty area and his shot is deflected off Hermoso and past a helpless Oblak.
15' - OFF THE POST! Athletic Club are agonisingly close to doubling their lead! Inaki Williams bends a delicious cross to the far post, it misses everyone, Oblak is rooted to the spot and can only watch on as the ball crashes off the base of the post!
45'+1 - CLOSE! Carrasco embarks on a lung-busting run, riding a couple of challenges as he closes in on goal. But his shot takes a deflection and he has to settle for a corner.
51'- OFF THE CROSSBAR! Griezmann rattles the woodwork with his free-kick! His five-month barren league run continues but that was a terrific effort!
56' - GOAL! ATHLETIC CLUB 2-0 ATLETICO MADRID (INAKI WILLIAMS, PEN): Oh, a Panenka! Cool as you like, Inaki Williams gambles on Oblak diving, which he does, and he clips it down the middle to double Athletic Club's advantage, leaving Atleti with a mountain to climb!
- Raul Garcia equalled Raul Gonzalez as the third La Liga player with the most games played in the competition ever (550), only behind Zubizarreta (622) and Joaquín (596).
- Atletico Madrid have conceded a penalty goal and scored and own goal for the sixth time in La Liga since 2003/04 campaign (D1 L5), three under Diego Simeone.
- Since the start of 2017/18, Mario Hermoso has scored four own goals (two for Espanyol and two for Atletico Madrid), more than any other player in the competition in this period (Paulo Olivera and Stefan Savic - three each).
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