Anthony Elanga proved pivotal, with the former Red netting the only goal of the game after just five minutes.
The Reds dominated the ball throughout the majority of the contest but often struggled to convert that into clear-cut chances.
Diogo Dalot hit the frame of the goal in the first half, while Harry Maguire saw his late effort cleared off the line by Murillo.
United must now dust ourselves off for Sunday's clash with Manchester City at Old Trafford, as Amorim said himself after the full-time whistle.
Scroll down to read what the boss made of our overall display in the East Midlands, as he spoke to various outlets, including TNT Sports and the BBC...