Ronald Koeman admitted Barcelona were not at their best as Ousmane Dembele scored an injury-time winner to sink 10-man Real Valladolid 1-0 at the Nou Camp.
Dembele volleyed home at the far post to seal his side's sixth straight LaLiga win and move within one point of leaders Atletico Madrid.
It was harsh on the struggling visitors, who looked set to hold out for a point despite the 79th-minute dismissal of Oscar Plano.
"We lacked more things in the first half," Koeman said in quotes reported by Marca.
"Our pressure on them has not been very good and, from the beginning of the game, we were a little slow, tired. We did not have control of the game.
"We changed the system and we improved in the second half. It was a difficult game.
"The team was far from their level. Valladolid did a good job defensively. You have to know how to suffer and we deserved to win."
Barcelona confirmed after the game that Philippe Coutinho had undergone surgery on a knee injury that is likely to rule him out of the title run-in.
Next up for Koeman's side are rivals Real Madrid on Saturday in an El Clasico with even more at stake than usual.
"They are two great teams in the world and a good result in El Clasico would be important for the title," Koeman added.
