Atletico Madrid's 100 per cent LaLiga record was emphatically ended on Saturday, as they lost 2-0 to a fired-up Real Sociedad in the first competitive fixture played at the Reale Arena.
Diego Simeone's side had managed three straight wins prior to the international break but turned in a below-par performance on the road, conceding two goals in a costly three-minute spell in the second half.
After a trio of away games at the start of the 2019-20 campaign, Sociedad excelled in front of a raucous crowd at their revamped home, albeit Martin Odegaard's opener owed much to a huge deflection off Stefan Savic.
They doubled their lead soon after through debutant Nacho Monreal, the former Arsenal defender seizing on a loose ball to poke home ahead of Jan Oblak.
Atletico's goalkeeper was injured in trying to prevent Monreal scoring and, after lengthy treatment on the field, was replaced by Antonio Adan, adding further to Simeone's concerns ahead of the start of the Champions League group stage in midweek.
Oblak had saved from Mikel Oyarzabal with an outstretched leg in a first half that saw the home side on top, while Savic denied Sociedad's captain when he inadvertently turned away an on-target header with his thigh.
Simeone sent on Marcos Llorente and Angel Correa in an attempt to turn the tide early in the second half, only for the visitors to be laid out by Sociedad's rapid one-two punch.
They had rallied from a two-goal deficit to beat Eibar at home last time out but were unable to complete a similar comeback on this occasion, Sociedad goalkeeper Miguel Angel Moya denying both Vitolo and Savic with smart saves to keep a clean sheet against his former club on a memorable occasion for the hosts.