Atletico Madrid's unbeaten run in LaLiga came to an end on Sunday when defender Jose Maria Gimenez scored an own goal in a disappointing 1-0 defeat at Real Betis.
Atletico now sit fourth in the Spanish top flight on 20 points, two clear of Betis, after their first loss of the season.
"I am clear on the path. I know that football is about work, and when you can't find that continuity and only achieve it in parts, you suffer," said coach Diego Simeone, whose side also suffered a crushing 3-0 defeat by Lille in the Champions League midweek.
Atletico were in trouble early on when Gimenez deflected Abde Ezzalzouli's cross into Jan Oblak's net, giving the home side the lead four minutes into the game.
Argentine duo Julian Alvarez and Rodrigo De Paul sought to create chances, as did Antoine Griezmann, but the best attempt came from Reinildo Mandava, whose header from a corner was brilliantly saved by goalkeeper Rui Silva.
Betis piled on the pressure in a bid to double their lead, particularly through striker Vitor Roque, who had a second-half goal disallowed for offside.
"We have to keep going, Barcelona are 10 points ahead of us, there's a lot left and we have to keep quiet, work harder in training and compete. The way forward is work and we're going to keep trying," Atletico captain Koke said.
Atletico face UE Vic in the Copa del Rey on Thursday before hosting Las Palmas three days later.