The Blues were a shadow of the side that has breezed through the past few months unbeaten and never got going in the opening period.
Within half-an-hour, City had lost the two-goal cushion from the first leg and from that point on, it was a long way back for Pep’s men.
“We played exceptional in the second half, but the first one we forgot to be there,” said the Blues’ boss.
“We are a team that wanted to defend aggressively without the ball. In the second half, it was much better but it wasn’t enough.
“Normally we play until half-time at a good level but tonight, we didn’t do that. It’s happened, the opponent was there and we will learn from this.”
Pep admitted the late Monaco winner, which came from a set-piece, was a killer blow - but felt by that time, his team should have been in control.
“We have a team with not much experience in this kind of competition,” he said. “At this level, when you concede and play the way we did in the first 45 minutes, it is so difficult. In the second half, we had the chances to score a lot of goals and we didn’t. That’s why we are out.
“In the first half, they could have scored more. Barcelona scored three goals through set pieces, two penalties and a free kick, so set pieces are important.
“That is my only sad thing - the way we played in that first 45 minutes. You can play and the opponent can beat you, but we were not there. In the right moment, we should be there but we weren’t.
“I think we will improve next year. We are going to try - of course we are. This competition is so demanding for the big teams.. In the special moments, we were unlucky. That’s why we will be looking to the Premier League and the FA Cup in the remaining months and then on to next season.”
