Barcelona midfielder Sergio Busquets apologised to the club's fans after his side were sent tumbling out of the Champions League in the semi-finals on Tuesday, losing 4-0 to a rampant Liverpool side for a remarkable 4-3 aggregate defeat.

It is the second year in a row Barca have thrown away a three-goal lead from the first leg to exit the competition, having been knocked out in the quarter-finals by AS Roma last season following a 3-0 surrender in the Italian capital.

"They were better than us, they went all out to win the game from the start and we really struggled with their pressure especially at the start of both halves," a despondent Busquets told reporters.

"I can't say anything else, all I can do is say sorry to our supporters because, after last year in Rome, to go out like this after such a good result in the first leg is very tough, there's little else to say."

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Barca looked on course to reach the final for the first time since 2015 after Lionel Messi inspired them to a 3-0 win in the first leg but they were overwhelmed by Liverpool's pressure and went behind in the seventh minute to Divock Origi's strike.

Busquets said his side were powerless to cope with Liverpool's pressing game.

"Once they scored and they pressed us high it was very difficult. I think we had the chance to score the goal that we needed but it wasn't to be," the midfielder said.

"When you face a team like this which presses you very high up the pitch and you don't make the most of second balls they just keep pushing further forward and with this atmosphere it was very difficult."

Substitute Georginio Wijnaldum scored twice in the space of two minutes early in the second half to level the tie on aggregate.

Origi then put Liverpool ahead in the tie for the first time thanks to some quick thinking from Trent Alexander-Arnold from a corner which caught Barca unawares.

"The fourth goal was a mistake from everyone as we were all taken by surprise. They were more clever than us to take the corner quickly and then they played by themselves," Busquets added.

"If we'd have scored it would have changed everything, we had the chances to do it, now it's very difficult to think of things to say."