Trailing 3-0, the Red Rebels clawed their way back into it and forced a replay with an incredible performance after the break.
The 3-3 draw was the game of the day anywhere and a derby match that had so much to it.
But the United boss laughed that it wasn't a masterstroke to introduce three new players.
"It was a mark of desperation more than anything really!" said the United boss on FCUM Radio.
"As a manager you don't want to have to make three subs at half time. You feel a bit sorry for the players who have had to be subbed but sometimes you are forced in making decisions.
"We really wanted to continue the fantastic performance we put in against Tamworth last Sunday but we didn't get off to a good start.
"When you come to Edgeley Park the first thing you want to do is quieten the crowd and make them nervous so things turn but it's fair to say we gifted them a 3-0 lead.
"It takes time when new players come in to get to know each other but that second half certainly helps.
"We are going to win games and we are going to lose games but what we are going to do is be able to look each other in the eye."
Now Marginson wants his side to compete the job.
"We have a belief in the dressing and we are standing shoulder to shoulder," he said.