Xabi Prieto struck a shock winner as Real Sociedad bolstered their bid for a Champions League spot with a 1-0 win at Atletico Madrid.
The Spanish midfielder raced onto Antoine Griezmann's clever pass on 53 minutes to place a low shot beyond Thibaut Courtois and claim a smash and grab triumph that brings a halt to Atletico's 100 per cent home record.
Diego Simeone's side were strangely out of sorts and were restricted to long-range shots for much of a low-key encounter.
The result leaves Atletico in third place, one point adrift of Real Madrid, while Sociedad move level with fourth-placed Malaga.
The Europa League winners came into the contest on a crest of a wave having enjoyed a recent run of impressive results that culminated in coach Simeone penning a new four-year deal to remain at the helm earlier in the week.
However, Real Madrid's 2-1 success at Celta Vigo meant they needed to stretch their 13-game winning run at the Vicente Calderon if they were to remain in second spot behind runaway leaders Barcelona.
The pressure was on and in the early stages they carved out a couple of half-chances against a nervy Sociedad rearguard.
Arda Turan, Cristian Rodriguez and Koke all let fly with shots that whistled just wide but it would prove to be as good as it got in a first period where the visitors grew as a force.
In fact, Philippe Montanier's men almost stole in front on 28 minutes when they put together the move of the half. Prieto overlapped on the right side of the penalty area and dinked a delightful ball to the far post where Griezmann's stabbed effort was well blocked by Courtois.
The Belgian stopper was a virtual spectator for much of the half and comfortably surpassed an 800 minute shut-out record on home turf that dated back to 1991.
The hosts were clearly frustrated and Turan was lucky not to receive his marching orders just before the interval when he followed up a yellow card with another reckless challenge on Carlos Vela.
Atletico improved after the break but were stunned on 53 minutes when Prieto raced clear to score with a low shot under Courtois. It was the first goal Atletico had conceded on their own patch since October and they struggled to recover following the setback.
Claudio Bravo had only been called upon to make some routine saves in the Sociedad goal but he did pull off a world class save late on, to ensure his team claimed all three points when he somehow kept out Falcao's deflected effort following Koke's free-kick from the right.
MAN OF THE MATCH
Xabi Prieto - Real Sociedad: Capped an industrious, hard-working display with a clinical finish that maintained his team's impressive run.
ATLETICO MADRID: Courtois 6, Juanfran 5, Miranda 5, Godin 5, Filipe 6, Turan 6, Koke 6, Gabi 6, Rodriguez 5, Falcao 5, Costa 5. Subs: Garcia 6, Adrian 6.
REAL SOCIEDAD: Bravo 7, Martinez 7, Gonzalez 7, Martinez 7, De la Bella 7, Bergara 6, Illarramendi 7, Prieto 8, Zurutuza 6, Griezmann 6, Vela 6. Subs: Estrada 6, Agirretxe 5, Ansotegi 4.