United won 3-0 on Sunday night via goals from Rasmus Hojlund, Alejandro Garnacho and Bruno Fernandes.
Amorim said afterwards: "I think it was good. I felt a little bit of a lack of energy, but they gave everything. Some players were tired but I think we deserved the win. We controlled the game. We could have been better with the ball but I understand after these two weeks. It was a perfect way to end this week with our away supporters. They are amazing."
On Hojlund's finish, he said: "A difficult goal with difficult control with his right foot. It's a shame we stop for the national teams biggest we have confidence."
Asked about Fernandes' performance, the manager continued: "He is a very good player, he is in a good moment, but what I like most is the way he works in every position to help the team."
And on Harry Amass' debut, Amorim added: "First of all it's his birthday so it is a special day. They have to understand they're so lucky to play for Man Utd. At the same moment I have so much fun putting young kids to play."