Chelsea goalkeeper Robert Sanchez and United goalscorer Casemiro were both sent off before halftime.
Afterwards, Amorim said: "We started the game really well, really aggressive. We were so aggressive in the second balls. We had the sending off with Casemiro, we like to complicate our game always but it was a good da! I felt the urgency, of course the sending off helped us. We had to be more clinical to finish the game off sooner.
"It is really important (the victory) because I understand the situation around this club. We cannot forget that we suffer a lot when we are on top. We can lose against Grimsby, we can beat any team. I'm just thinking about the next one. It is really good to win. We need the urgency to win again, that is really important for us."
Bruno Fernandes opened the scoring and laid on Casemiro's goal.
Amorim said of his captain: "He has a great spirit, he is our captain and he scored a goal playing as a midfielder so I am really happy about that! People don't have good things to say about our team so I am just joking around! I have nothing to say to the critics and, most of the time, they are right. Today, we won and it is a good day for us."