Rashford scored twice, as did Josh Zirkzee, for the comfortable victory.
He said afterwards: "The energy and the atmosphere speaks for itself. It is down to the players to create this in the stadium but the fans today, that is what we want to hear, nothing but positivity and pushing the fans forward.
"It wasn't as easy as it looked today. Amad did well to counter-press for two of the goals. He's so sharp and he's always got the intent to push the other team back, with and without the ball. It is for the players to understand the strengths of other players so we can feed off each other.
"We worked on it (the first goal) yesterday and it is always nice when something comes off that you worked off. It was a nice goal. The all-round team performance and energy and atmosphere is what we want to create because it makes it difficult for teams to beat us.
"He (Ruben Amorim) is definitely demanding but encouragement to bring your strengths into the game. That is when you get a really good team performance. Hopefully we can build on this and keep pushing. It's nothing to get overly excited by. We have to keep pushing every day to meet his demands."