Claudia Pina gave Barcelona the lead with their 14th shot of the game
Manchester City manager Gareth Taylor described his side as "a little bit dysfunctional" as they lost at Barcelona in the Women's Champions League.
Trophy holders Barcelona dominated the game and earned the comfortable win they needed at the Olympic Stadium to top Group D.
Inspired City goalkeeper Khiara Keating kept the hosts out until the 44th minute, when Claudia Pina slammed into the bottom corner following a goalmouth scramble.
Barcelona needed to win by two clear goals to finish above injury-hit City in Group D, having been beaten 2-0 in Manchester in October.
They got the second goal they craved early in the second half when Aitana Bonmati shrugged off Leila Ouahabi and finished through the legs of Keating.
The third arrived in the 69th minute as substitute Alexia Putellas scored with a low shot from long range past the unsighted Keating.
Afterwards Taylor praised his team's effort and said the loss would not change their course - while admitting they had been below their best.
"We know we weren't functioning and effective in certain areas with and without the ball, but you couldn't fault the effort of the players," he said.
"This game won't define us. We'll learn, get better, get players back, start to get stronger and will improve.
"We were a little bit dysfunctional with and without the ball tonight, but the effort from the girls was first class."
Both sides were already guaranteed to progress to the Champions League quarter-finals, and they each finish on 15 points - but Barcelona take first place.
They topped up their goal difference to +23 in doing so, while City finished with +5.
City's defeat - their second in four days after a league loss at Everton on Sunday - drops them to second in Group D and means they could face a tougher draw for the knockout stages.
'We had a thorn in our side'
City had got their maiden Women's Champions League group campaign under way in some style when they beat Barcelona at Joie Stadium.
Things have changed in the weeks since, however. While Barca have won all of their 12 games across every competition, City have struggled with form and injury blows.
Manager Taylor could name only eight substitutes in Spain, including two goalkeepers and three teenagers. Key figures Khadija Shaw, Alex Greenwood, Vivianne Miedema and Lauren Hemp are among his most notable absentees.
Barcelona smelled blood, their attacking starting XI featuring forward Esmee Brugts at left-back, and Ballon d'Or winner Bonmati admitted afterwards that revenge was also a factor.
"We had a thorn in our side from the first game against City," the Spanish midfielder said.
"That one came a little bit too soon for us; we weren't ourselves that day, I honestly think that City were superior. So we came into this game absolutely determined to show who we are and to put that right."
Barcelona overwhelmed the visitors at times in racking up 75% possession and 30 shots.
City did serve their hosts with a couple of scares. As Chelsea proved in the semi-final last season, Barcelona can be punished at the Olympic Stadium if they do not take their chances. The biggest fright came when Jill Roord rattled the crossbar from distance after 37 minutes.
But the gap in quality was shown by Barcelona going two up through superstar Bonmati - and Taylor responding by subbing on 18-year-old Lily Murphy.
Home boss Pere Romeu was also able to send on a two-time Ballon d'Or winner in Putellas to secure the win.
For Taylor, the main saving grace from this game may be that it was City's last of 2024, as they enter the WSL winter break.
'Outstanding' Keating saves City's blushes
Manchester City keeper Khiara Keating kept the scoreline respectable with a series of great saves
Taylor named an unchanged City side from the Everton game, including Keating in goal.
Keating has had a mixed season since her breakthrough last year, sharing the gloves with Ayaka Yamashita and looking from the outside as Mary Earps and Hannah Hampton have battled for the England jersey.
But here she kept City from being embarrassed with a series of terrific saves, making 14 in total.
"She's been ready and available and that's all you can be as a keeper," said Taylor of Keating.
"She was outstanding tonight, showed a lot of personality and a lot of maturity for someone so young on the biggest stage."
Keating's busy night started in the fourth minute with a low stop from Salma Paralluelo.
She tipped a Brugts effort over the top in the first half and made three fine stops to deny Ewa Pajor.
There was nothing she could do when Pina finally broke the deadlock one minute before the interval, but she was back in form just 20 seconds after the break to palm away another effort.
Her passing was less secure, giving the ball away several times. Bonmati nearly lobbed Keating from distance following a loose pass, with the goalkeeper grateful that the effort bounced wide.
Ultimately, Keating did well to keep the score down against a Barca side who scored 26 goals in their six group games.
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