Xavi Hernández labelled Barcelona's performance against Real Sociedad as unacceptable and blamed it on an El Clásico hangover despite coming away with a 1-0 win from the Reale Arena.
Ronald Araújo headed in the only goal of the game in the 92nd minute to seal the three points after a match that had been dominated for large parts by the home side.
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Xavi conceded that La Real deserved more for their performance and criticised his own team's display, saying the players had been knocked by last week's 2-1 defeat to Real Madrid.
"The first 25 minutes were unacceptable," the Barça coach said in his post-game news conference. "It's the opposite to last week, when we played well and deserved to win but lost. Today is a day to be really self-critical.
"La Real are a great side and they showed more intensity than us. We were not at all comfortable. We had a hangover from El Clásico. We were more affected by that result than I thought."
Barça were thankful to goalkeeper Marc-André ter Stegen early on as La Real flew out of the traps in San Sebastián, forcing the German into a string of saves.
Ander Barrenetxea, Mikel Oyarzabal and Take Kubo were all denied by Ter Stegen as the first half ended goalless.
"At the break, I asked [the players] if they were tired and they told me they weren't," Xavi added. "So I told them they have to play with more intensity. It was as simple as that.
"In the second half, we were a bit better. A draw is never enough for us. We made attacking changes to win the game and finished strongly.
"We were physically good in last 10 minutes. The team felt more comfortable and we created chances, with Gavi coming close and then Ronald getting the goal.
"Sometimes football is unexplainable. Last week, we deserved to win and didn't; this week, we end up winning when maybe we did not deserve it. That's football."
The win keeps Barça within four points of surprise leaders Girona, who beat Osasuna 4-2 earlier on Saturday, and moves them one behind Real Madrid, who play Rayo Vallecano on Sunday.
Real Sociedad, meanwhile, slip to sixth in the table after failing to take their chances.
"The fans can be proud of how we played, but as coach and players we are angry," La Real boss Imanol Alguacil said in a news conference.
"It's no good for me if opposition coaches are saying we were the better team when we have lost. I am tired of hearing praise when we have been beaten.
"We have to win games when we play like this. When you are on top, you have to kill off the game. We have to be self-critical because this has happened in many games now."