Nineteen-year-old Edgar only played because former United midfielder Nicky Butt was forced to withdraw with an ankle injury two hours before kick-off.
Glenn Roeder: "It was very, very pleasing to see that ball hit the back of the net, it goes without saying. Every person has dreams in their life and for very few, those dreams come true.
"I would say today for David Edgar and his father Eddie, who was here to see his son play, that is one of the few occasions when a dream has come true.
"I said to them before the game and I reminded them of it afterwards, anything is achievable in life. I would say that is as well as Newcastle have done against Manchester United for a while. I like to think the fans have seen a good game today and have gone away happy.
"I am a greedy person and it would have been nice to have taken three points, but in the circumstances, losing Nicky Butt two hours before kick-off - and he was so upset about that - we know it is a very good point."