Atletico Madrid were beaten at home to Villarreal on Sunday with an 85th minute strike from Luciano Vietto.
The 21-year-old striker broke past Diego Godin and placed the ball beyond Miguel Angel Moya sixminutes from time in a game that Diego Simeone's side struggled to get a grip of.
The result means the defending La Liga champions were unable to capitalise upon Barcelona's goalless draw with Getafe on Saturday.
A win would have seen Diego Simeone's side go level with Barca in second place, but the visitors produced an organised display to pull off the shock victory.
Villarreal were denied a penalty in the first half when Gabi appeared to nudge the ball out of the way of Ikechukwu Uche on the stroke of half time with his arm.
In truth Atletico had the better of the chances, but Villareal denied them too many clear-cut opportunities during a lack-lustre first half.
And the visitors began the second half spiritedly, as the lively Vietto ran at Atletico's defence on 52 minutes and shot narrowly wide from the edge of the area.
Mario Mandzukic then had a header ruled out for an innocuous challenge on defender Mario as Atletico looked to hit back at Villarreal's pressure.
But it was the visitors who stole victory when Vietto beat Godin and finished stylishly to secure the three points.
