The 18-year-old scored two second-half goals on his full Premier League debut to help the reigning champions overturn a 1-0 deficit at the Stadium of Light on Saturday.
Januzaj, who has been linked with a move to Manchester City in recent weeks, is delighted with his start to the season and vowed to continue improving at Old Trafford.
“I’m really enjoying myself,” Januzaj told Daily Mirror.
“I played quite a few games in the reserves last season and thought I did well.
“From there, I had the chance to go on the summer tour and it was a good opportunity for me to show what I can do for the team. It was a great experience and ever since I’ve been working hard.
“When a big, big manager like Sir Alex Ferguson gives you a shirt number your thought is that you can really do something for this club.”
“When you realise everyone is behind you at Old Trafford, it gives you the belief to play with the qualities I have.
“It really helped having that support behind me because you get a feeling that everyone wants you to do well.
“I want to play in as many games as I can and become the best player I can possibly be. I know that I need to keep working hard every day to achieve that. I have to be ready, ready to take my chance.
“I’m confident in my ability and believe I can help the team.”
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