Luis Enrique bemoaned the error that led to Manchester City's equalising goal in a 3-1 Champions League defeat at the Etihad Stadium, claiming the incident was the turning point in the match.
Lionel Messi fired Barca in front after 21 minutes, but a loose Sergi Roberto pass across the defence led to Ilkay Gundogan's 39th-minute leveller.
Kevin De Bruyne gave City the lead from a free-kick following a bright start to the second half, before Gundogan wrapped up the win 16 minutes from time.
The win represents a measure of revenge for Pep Guardiola's side, who were beaten 4-0 by their manager's former club at Camp Nou a fortnight ago.
"I think [the first 40 minutes] was one of the best 40 minutes that we've played, particularly on a stage like this against a top-quality rival," said Barca head coach Luis Enrique. "We played really well.
"It's a shame that after the error we made for the first goal, from there on we had a bad time.
"When you concede a goal in that way it's normal that you go through a bad period."
Luis Enrique did, however, reserve praise for City's high-tempo, high-pressing approach to the second half.
"In the second half we hoped to dominate the game but it couldn't be because of mistakes that we made and pressure from the opponent," he added.
"City took advantage of our errors. They have some quality players. They pressured aggressively and provoked more errors from our team than we did from them.
"We need another four points to qualify and that's what we have to focus on."
Referencing the absence of key players such as Andres Iniesta, Jordi Alba and Gerard Pique through injury, Luis Enrique commented: "If you lose it is not because of the players that are not there.
"You have to look at what happens on the pitch. It's not surprising and nothing strange - it doesn't just happen to Barcelona."
The result leaves Barca two points clear of City at the top of Group C after four matches.