Moises Caicedo struck to cancel out United's opener scored by Bruno Fernandes.
Van Nistelrooy said afterwards: "Overall it was a very good performance. The players did really well and fought in every inch of the pitch. It was very good to watch that bit.
"Overall the chances we created, we could have scored one more to win the game. It was a shame we couldn't. Overall I'm slightly disappointed we didn't win.
"It's an emotional rollercoaster - it's been almost a full week where so many things happened. My job was to steady the ship. The players reacted very well, something to build on in the next two games.
"I came here to help the club in any capacity. After these two games that will continue and hopefully it can work out.
"It's special to be back in the city and at the club. I really enjoy every single minute of it.
"I try to share the culture of the club, the culture of the town and the fans. That's an important part. I'm glad I can share these moments and help the players understand the spirit.
"I saw the spirit on the pitch on Wednesday and today. That's the foundation to grow."