I have seen too many football matches not to know sometimes teams don't start at 100% in important games. That's acceptable.
But Pep made changes, the team did perform 2nd half and we were through after we scored!
20 min left to play, Monaco already tiring as you said.
That was the moment to get Yaya on (for Sterling, shift KDB out right) and control the match.
Also Zab on for Sagna like we did in the 1st leg and because we know we always can rely on his spirit.
Those changes would have been a strong shout for the Blues and for Monaco as well.
Well, hindsight. Would be interesting to know, why Pep didn't make those changes.