"It wasn't our best day. We needed to compete at a bit more of a higher level. Above all defensively we gave too much away — the proof is the three penalties we conceded and the two goals from shots outside the box," the Asturian coach said.
José Alberto made eight changes to his starting line-up, a decision he took full responsibility for.
"I believed the team could compete at a better level, but we weren't able to. With three games this week, I wanted to give minutes to players who have had fewer of them, because otherwise it's very difficult to do," he explained, while insisting "everyone put in a shift" even as the team needed to be "tougher."
He described a familiar pattern whenever Racing threatened to close the gap.
"The feeling I have is that every time we threatened to cut the deficit, they hit the accelerator again and pulled away. They're in an extraordinary moment of confidence that's very hard to stop," he said, noting his side were effectively still doing pre-season work with the campaign already under way, given the number of new arrivals in the squad.
Hansi Flick, by contrast, was delighted with a performance he felt went beyond the scoreline.
"I like how we're playing, the result... I'm happy. The team is happy, it wasn't so easy to play against Racing, they play good football and want the ball. We deserved the result," the Barcelona coach said. Flick praised the collective mentality behind the win, and singled out new signing Karim Adeyemi's contribution after a difficult spell in Germany.
"Adeyemi gives us a lot, and he's a lad who's well liked in the dressing room. He has great speed," Flick said.
Asked about Wojciech Szczęsny's error in goal, with first-choice Joan García sidelined by a knee issue, Flick was unconcerned.
"It's normal to make mistakes, this is football. Everyone makes mistakes — the goal they scored wasn't necessary, but neither was the first one. These are things we have to work on," he said, adding that Joan García's fitness would be assessed the following day.
Flick declined to rank the squad against his previous Barcelona sides.
"It's not easy to compare with previous teams, I don't like doing that," he said. "We haven't won anything yet. We have to work and put in the effort. We're on the right path, and we have to keep going."