Atletico Madrid's 2-0 defeat at Celta Vigo was "the best thing that could happen for us" according to Atleti boss Diego Simeone.
Ten-man Atletico were handed a humbling first defeat of the new LaLiga season in a dismal display at Celta Vigo, going down 2-0 at the Balaidos.
Maxi Gomez netted the opener in the 46th minute and then created the second for Iago Aspas in the 52nd as Atleti failed to recover from a poor first half in which they lacked cutting edge up front. A third goal ruled out by the video assistant referee.
Atleti, who are being tipped by many for a strong title challenge, had Stefan Savic dismissed for two yellows.
Maxi Gomez scored Celta Vigo's first goal
"I'm not worried about the result," said Simeone.
"I'm calmer than ever, because this is a wake-up call for us. We didn't play well and Celta were lethal.
Atletico, champions in 2013-2014 and runners-up last season, have four points from three games going into the international break.
It was a frustrating night for Antoine Griezmann and his Atletico teammates against Celta Vigo
Antoine Griezmann sought to inspire his side, but a fightback never looked likely for Diego Simeone's men, who were tipped to put up a decent fight for the title.
Indeed, things went from bad to worse for Atleti as Stefan Savic saw red with 20 minutes remaining, although Gustavo Cabral was harshly denied a third by a marginal offside call after a VAR consultation.
After an open yet uneventful first 25 minutes in which the two sides took turns to counter, Griezmann was inches from firing Atleti in front as a 20-yard drive crept wide.
There was little incident of note in the remainder of a sweltering first half, but Celta took just 42 seconds to break the deadlock following the restart.
Gomez pounced on Diego Godin's slip to hammer low into the net and Atleti were quickly stunned by a second blow, the first goalscorer turning creator with a lovely delivery onto Aspas' head.
Savic was then dismissed for a second yellow card as he handled the ball to concede a free-kick from which Cabral thought he had added a third, before a lengthy VAR delay saw the defender judged offside.