The former Ipswich midfielder, not renowned for his aerial ability inside the box, popped up with the goal that knocked out Sheffield United with six minutes remaining.
The man of the match had helped cancel out the Blades' 1-0 lead from Friday with a splendid through ball for Kevin Dawson's opener after five minutes.
And Johnson revealed that he told the long-serving Upson of his disappointment at his first-leg display.
"We've been talking about heroes and villains and there was a villain out there who turned into a hero which was fantastic," he said.
"He (Upson) was one of those who had a bit of a lack of concentration in the first-leg that led to their goal.
"He thought I might have left him out all week, along with a couple of others. But I gave those villains the chance to be heroes and that is what they did.
"Ed came up with something and credit to him. His mum and dad didn't call him Ed for nothing! I love them all to death and when I smack them I feel very sad, it is like smacking your little un, you don't really mean it!
"But I may have to smack them a bit more to get our promotion because we've come this far - we have to get this promotion now."
- Sheffield United