The Dutchman allowed his players the freedom to express themselves last night.
United were 5-2 winners over Leicester City in the Carabao Cup fourth round at Old Trafford on Wednesday.
Speaking to MUTV pre-match, Van Nistelrooy said: "We had to deal with a day like yesterday and give the players some space to get their heads around things and their emotions.
"Then they needed to switch their mindsets to performing and that is what we did today. We wanted to focus on seeing an energetic, an attack-minded performance, having a lot of the ball, and attempting to give the crowd a great night.
"It has been a couple of days of mixed feelings," Van Nistelrooy added.
"When you see a colleague go, it is a big disappointment.
"Erik (ten Hag) brought me in and in the first conversation we had, what struck me most was the passion he had for Man United, and I experienced that with him. He was really fighting for this club, for the supporters, and that was what brought us together."