The forward scored the crucial final penalty as United beat Arsenal in the FA Cup third round.
After the tie went to extra time following a 1-1 draw, United hung on over the added 30 minutes with ten men, before winning the shootout.
Post-game, Amorim stated: "Yeah, it's really important, not just for him, but for all the players. Your life as a footballer has cycles, and moments, and sometimes in one week, your life can change. And you can see Altay (Bayindir) - against Tottenham, everybody was like pointing the finger for Altay, and I understand that.
“And today, he was our hero, also. Joshua, (a) few weeks ago, had a small problem with our fans and today, every time he's going on the pitch, you feel the support from the fans and then he has the last penalty. So, the life is like that and you have to continue (to be) humble, to work every day. Your time will come. And so it's really important for them. Not just for them, but for his team-mates."
He added on whether he worried Zirkzee could step up in that moment: "I was not, because I had the feeling that we are going to win, but that part is not my part.
“The set pieces is not my part, and today we were amazing in set pieces. So Carlos (Fernandes) was really good. Andreas (Georgson) was really good. Emanuel (Ferro) was really good, and they chose the right players to score the penalty. So, it's not my part, it was them. They did a very good job."