Tbh, I rewatched Willian's shots. First one is Busi's fault. He is there in time but he is slow in 1 vs 1. He was always better at stoping players before they get in possession than at winning 1 vs 1s. So for the first shot, Willian is just quicker, he beats Busi and takes a great shot.
For the 2nd, you have Roberto doing one of his stupid clearances that you just don't know where they're gonna land. It lands to Willian, who is great again at shooting almost without any preparation. Just quick touch and shoot. And with power not some mellow attempt.
For the 3rd, this is just a tactical fuck up, probably from Busi as well. You just don't go overcrowding the box because a smart player like Hazard is not just a crossing robot like Deulofeu. As soon as our players anticipate the cross, Hazard sees Willian unmarked, who does what he did in the first two chances only better.
So, I blame Busi and Roberto for most of the defensive problems in this game.