I final finished the game, which I feel very different from the comments here.
The team was probably trying to reserve energy for the Derby, every time they led they slow down the tempo and ease the intensity, and try to control a bit more.
It can also be complacent, like we are very close to winning the scudetto, but still the first goal was exactly how we did it this season, the team is still there.
Ranieri actually did a great job, he knows his team is inferior, so there weren't a lot of attempts in build up or complicated pressing.
He kept the plan simple and it was effective with some luck.
The attack was the cream, they almost only need to win the first long ball contact or break of the CB and let someone else shoot, typical classical English 2 strikers method, what is concerning is Acerbi is showing signs of not being himself for not dominating the challenge. (Cannot have a conclusion on what is causing it)
Not to mention, the second goal was kinda handball.
All in all, I don't buy the theory we got devasted after Atletico, nor we are so low on energy.
I think we could have avoid the tie, btw getting a 2 goals lead, but it is nothing like the team has collapsed or something super negative that we will collapse next season etc.