Fletcher was a late substitute on the day as he followed twin brother Jack in making his debut for the club.
Fletcher told MUTV: "It's a mad day. I'm absolutely buzzing. The best day of my life, it's a dream come true. I've just got to thank everyone for supporting me, throughout the way.
"It's an honour to have one of those (academy) numbers. Not many people do it. I'm grateful it's happened. To get to go on the pitch and play at Old Trafford, it's a special feeling."
Tyler also said: "I found out I was in the squad yesterday, after the session. I got told you will be with the first team, you'll be on the bench. I was buzzing with that.
"I was warming up in the last five minutes and five minutes got added on. I got the call and I was like: 'No way is this happening'.
"I was told to go and enjoy it and make as many passes as you can, get as many touches as you can, and that's what I did."