Match ends, Celta de Vigo 2, Atlético de Madrid 0.
Atletico Madrid had former Manchester City defender Stefan Savic sent off as they were beaten at Celta Vigo.
Celta were leading 2-0 when Savic was dismissed with 20 minutes remaining after being shown a second yellow card on a bad day for Diego Simeone's side.
The hosts took the lead through Maxi Gomez before former Liverpool forward Iago Aspas doubled the lead with his first goal of the season.
Celta had a third goal overturned by the video assistant referee (VAR).
Argentine defender Gustavo Cabral was denied by a marginal offside call.
Atletico, champions in 2013-2014 and runners-up last season, have four points from three games going into the international break.
Victory propelled Celta to the top of La Liga before second-placed Real Madrid's home match with Leganes later on Saturday.
Celta, who have never won La Liga, have seven points from three games.
Match ends, Celta de Vigo 2, Atlético de Madrid 0.
Second Half ends, Celta de Vigo 2, Atlético de Madrid 0.
Attempt missed. Antoine Griezmann (Atlético de Madrid) left footed shot from the right side of the box is close, but misses to the left.
Attempt missed. Fran Beltrán (Celta de Vigo) right footed shot from outside the box is too high. Assisted by Sofiane Boufal.
Brais Méndez (Celta de Vigo) wins a free kick in the defensive half.
Foul by Santiago Arias (Atlético de Madrid).
Attempt saved. Néstor Araújo (Celta de Vigo) header from the centre of the box is saved in the bottom left corner. Assisted by Hugo Mallo with a cross.
Maxi Gómez (Celta de Vigo) wins a free kick on the right wing.
Foul by Filipe Luís (Atlético de Madrid).
Foul by Diego Costa (Atlético de Madrid).
Facundo Roncaglia (Celta de Vigo) wins a free kick in the defensive half.
Substitution, Celta de Vigo. Sofiane Boufal replaces Iago Aspas.
Offside, Celta de Vigo. Okay Yokuslu tries a through ball, but Hugo Mallo is caught offside.
Corner, Celta de Vigo. Conceded by Saúl Ñíguez.
Attempt missed. Fran Beltrán (Celta de Vigo) right footed shot from outside the box misses to the left. Assisted by Maxi Gómez.
Diego Godín (Atlético de Madrid) wins a free kick on the right wing.
Foul by Iago Aspas (Celta de Vigo).
Saúl Ñíguez (Atlético de Madrid) wins a free kick in the defensive half.
Foul by Maxi Gómez (Celta de Vigo).
Substitution, Celta de Vigo. Brais Méndez replaces Stanislav Lobotka.
Foul by Nikola Kalinic (Atlético de Madrid).
Facundo Roncaglia (Celta de Vigo) wins a free kick in the defensive half.
Attempt saved. Hugo Mallo (Celta de Vigo) right footed shot from a difficult angle on the right is saved in the top right corner. Assisted by Okay Yokuslu.
Delay over. They are ready to continue.
Delay in match (Atlético de Madrid).
Hugo Mallo (Celta de Vigo) is shown the yellow card for a bad foul.
Antoine Griezmann (Atlético de Madrid) wins a free kick on the left wing.
Foul by Hugo Mallo (Celta de Vigo).
Corner, Atlético de Madrid. Conceded by Néstor Araújo.
Okay Yokuslu (Celta de Vigo) is shown the yellow card for a bad foul.
Santiago Arias (Atlético de Madrid) wins a free kick on the right wing.
Foul by Okay Yokuslu (Celta de Vigo).
Delay over. They are ready to continue.
Delay in match (Atlético de Madrid). Video Review.
Offside, Celta de Vigo. Hugo Mallo tries a through ball, but Gustavo Cabral is caught offside.
Second yellow card to Stefan Savic (Atlético de Madrid) for hand ball.
Hand ball by Stefan Savic (Atlético de Madrid).
Substitution, Celta de Vigo. Okay Yokuslu replaces Pione Sisto.
Substitution, Atlético de Madrid. Santiago Arias replaces José Giménez.
Attempt missed. Pione Sisto (Celta de Vigo) right footed shot from the centre of the box misses to the left. Assisted by Iago Aspas.