A Lionel Messi penalty separated the two teams.
"It's an 11 that competed very well against Barcelona," Imanol said.
"We came into [the game] after a big effort [against Mirandes in the Copa] and we only had a few days [in between].
"[The players] are all in good form and today they showed that today.
"The team is competing well and is able to take on Barcelona in their own stadium.
"Unfairly, we left with a defeat. We deserved at least a draw."
Barcelona were whistled by their own fans at times during the game and Imanol was pleased with his team's contribution to that.
"Our team did a great job and, if Barcelona weren't at their best, it's because we did things well," he noted.
"We watched videos on their latest matches. We took risks.
"What we did has a lot of merit. We hurt them in the transitions."