The flurry of switches - four of the five coming before the hour mark - may have prompted some to think that Amorim wasn't happy with what he was seeing, but the head coach gave a different view.
Speaking to TNT Sports after the game, he said: "I think we did like four substitutions because of the fitness of the players, not thinking about what is best for the game.
"We are in that moment. We need the squad all together fit, and you have to take some risks and that's it."
That the new United boss clearly already has a strong focus on the condition of the squad, given the scale of injuries in recent times, will put many Reds' minds at rest.