Amad created United's opener, scored by Bryan Mbeumo, and impressed at wing-back. Lammens, meanwhile, made several significant saves, including to deny Alexander Isak in the first-half and Cody Gakpo after the break.
Amorim said of Amad: "Amad is doing so well in that position. He's perfect for that position. He was upset today when I made a sub, but he was on a yellow card, it was a lot of man to man on the side, so it was just about that.
"If not, he would continue with the game because he is so important for us. He has struggle for a few weeks (with his bereavement), but we are here for him and that's the most important thing."
On goalkeeper Lammens, he added: "He was really important. Sometimes it is a little bit of luck because they had two shots on the post. That can change the narrative, the way you see the team, the goalkeeper or whatever. So we have to understand that, but he showed a lot of character, a lot of quality and we win also because of Lammens."
Amorim also stated, "I think that was the biggest win in my time at Manchester United. It means a lot today but tomorrow it won't mean a lot. It's three points and it's a good victory."