Everton won 1-0, with Idrissa Gueye sent off before halftime after clashing with teammate Michael Keane.
Asked if the absences of injured pair Matheus Cunha and Benjamin Sesko was a factor, Amorim stated: "Of course, when you have more players with different characteristics, especially with Cunha or Ben, you have more options to score goals, especially against low blocks where there’s no space.
"But that is just an excuse, we have players on the pitch, and we could lose the game but with a different intensity, the understanding of the moment when the other team fight each other and get the red card. And I think we didn’t understand the moments of the game during the 90 minutes.
"That is my fault, that I need to be better to explain the players how to play in every situation of the game. Again, I think they start the game with a different intensity and that was really hard for us."