Sergio Busquets took his share of the blame for Barcelona's stunning 4-3 defeat to Celta Vigo and pledged to work harder to get the La Liga champions back on track.
Luis Enrique's side headed into the match at Balaidos aiming to go top after Real Madrid drew once again against Eibar on Sunday.
But the loss leaves them fourth, with Atletico Madrid's victory over Valencia earlier on Sunday meaning Diego Simeone's men the lead the way from their city rivals, with Sevilla in third.
"Clearly I am one of those responsible for this defeat," said Busquets, as quoted by AS, after being selected in an unfamiliar midfield three with Arda Turan and Andre Gomes.
"I have not done one of my best matches and when you are in an important area in the field, an error penalises you a great deal.
"We must try again to become the team that wins games. We have won titles and have been the best in the world.
"We are not robots, we are not machines. Sometimes it is a positional fault by poor control. It is clear that I am one of the guilty ones and just have to work harder."
Celta were rampant before half-time as Pione Sisto, Iago Aspas and a Jeremy Mathieu own goal made it 3-0, prompting the introduction of Andres Iniesta for his 600th Barca appearance.
Gerard Pique headed one back from Iniesta's cross and Neymar scored a penalty before a dreadful error by goalkeeper Marc-Andre ter Stegen allowed Pablo Hernandez to make it 4-2.
Pique reduced the arrears again to set up a grandstand finish, but Barcelona fell short and Busquets added: "We know that the level at which we must reach is high. The first goal penalised us a lot and then we conceded two more.
"We were poorly positioned, we made mistakes. We wanted to turn the game but the goals penalised us."
