Man United confirmed on Friday that they had reached an agreement to appoint the Sporting Lisbon manager as their new head coach.
The Red Devils will pay €11m (£9.25m) to recruit Amorim and his staff as they prepare for a new era under the Portuguese manager.
Amorim will officially take over the reins at Old Trafford on November 11, leaving him to lead Sporting until the next international window.
On Friday evening, Amorim took charge of his first match since his Man United appointment was confirmed as Sporting played host to Estrela Amadora in a Primeira Liga clash.
Amorim claims Man United rejected key demand
Prior to the match, Amorim received a standing ovation from the majority of the fans in attendance at the Estadio Jose Alvalade.
However, he was the subject of a harsh banner left outside the stadium which read: "Amorim, this is no longer your home, thank you!!"
Viktor Gyokeres played the starring role when the game got underway, scoring four goals to help his side clinch a 5-1 victory.
Speaking after the win, Amorim revealed he took three days to make a final decision over his future and had even asked Man United whether he could delay the move until the end of the season, but his request was ultimately denied by the Premier League club.
Amorim told reporters: "The situation is: at the beginning of the season, I had a talk with him and Hugo Viana [then-sporting director] and I said that whatever happened, this would be my last season with Sporting. The president is here, he can confirm that.
"The season started, we know that we started very well. Then the Manchester United situation came and they appeared. They paid above the release clause.
"I never discussed anything with the president about this bargaining. The only question I made was only to go at the end of the season.
"For three days, I said I wanted to stay until the end of the season. But I was told it was not possible, I was told it was now or never, or Manchester United would go for another option.
"I had three days to make my decision. The change is radical in my life but I had three days to make this decision. That's what I did."
Amorim "wanted" Man United opportunity
While Amorim has spent time deliberating on his future, he was clear that he is looking forward to taking on the challenge of turning Man United into a force to be reckoned with.
Amorim added: "I have had other opportunities, the president and Viana can confirm this is not the first or the second time I was asked for by another team.
"I wanted that one in Manchester. I want that context. That context allows me to do things my way. It's just like Sporting.
"There's time when I have to take the step forward. It was harder for me than for any Sporting fan but I had to do this."
Amorim will lead Sporting in their next two matches against Manchester City and Braga in the Champions League and Primeira Liga respectively.
Once those two games are completed, he will bid farewell to the Portuguese giants and begin life as a Premier League head coach.