The Dutchman took charge of United on an interim basis in midweek against Leicester City.
The Red Devils were able to get an impressive 5-2 win at Old Trafford against the Foxes to move into the quarter finals.
Post-game, Van Nistelrooy told MUTV: "I couldn't ask for more. The first goal was an unbelievable, top corner and a fantastic finish. Then was also some luck today, I have to say.
"We had luck on our side with the double post, coming back to Casemiro and the Bruno deflection, but delighted for him because the first one went in. Then you see more goals coming.
"So delighted for him as well. A good goal from Garna and a good assist from Diogo and what was the other one? Have I covered all five goals? It was a great night."
"I was delighted for Casemiro. The way he's been training and helping the team, the club, it's such an example," he added.
"You also see the crowd's reaction and they know what he's about. I'm delighted to have him around and going through difficult moments, he got a lot of criticism after the Liverpool game. It's so hard, he was almost the one to blame for that game and it's not fair, he didn't deserve that and it's totally not true.
"If you see him train and prepare for games, with the history and all he's achieved with five Champions Leagues, he's an example for us and that was part of my celebration - I was happy for him.”