Diego Simeone's team followed up their home loss against Lille in the Champions League with a 1-0 defeat at Real Betis in the Spanish league on Sunday.
An own-goal by defender José María Giménez less than five minutes into the match sealed Atletico's second consecutive loss.
They have only one win in their last six matches in all competitions - a 3-1 victory over Leganes in the Spanish league last weekend. Before that, they had league draws at home against Real Madrid and at Real Sociedad, and lost 4-1 at Benfica in the Champions League.
"We know what we have to do, what we need to work on," Simeone said. "It's clear to me that soccer is all about getting the work done and when you can't find that dynamic you end up suffering."
On the plus side, Atletico had been unbeaten in 11 consecutive league matches until Sunday's defeat in Seville.
"We weren't able to play the type of game we wanted to play," Simeone said. "They got off to a strong start and were lucky to get the early goal."
Giménez found his own net while trying to clear a low cross into the area in the fourth minute at the Benito Villamarin Stadium.
The loss kept the Madrid club in fourth place, one point behind third-place Villarreal and four points behind city rivals Real Madrid, who lost 4-0 to Barcelona at home in Saturday's clasico.
Atletico are 10 points behind leaders Barcelona after 11 rounds.
Betis moved to fifth place and two points behind Atletico. Manuel Pellegrini's team have won five of their last eight league matches, including two of their last three games.
It was only Betis' second home win against Atletico in their last 16 league matches, and the first since 2019.
Sixth-place Osasuna picked up first-half goals in a 2-0 victory at Real Sociedad to end a two-game winless streak. Sociedad dropped to 12th place.
Leganes scored three second-half goals in a 3-0 win over Celta Vigo, while Getafe converted a 90th-minute equaliser in a 1-1 home draw against last-place Valencia, who are winless in five consecutive matches.
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