Iron manager Brian Laws branded his side 'too cocky' after seeing his side throw away the lead twice during Saturday's reverse at Kidderminster.
The home side, who were bottom in the table going into the weekend's game, twice came from behind to equalise and Kevin Langmead scored a late winner in second-half stoppage time.
The goal moved the Harriers off the bottom of the table, and denied United the chance of reclaiming the top spot.
Instead, Leyton Orient surged to the top of the table thanks to their 4-1 demolition of Shrewsbury Town.
The result left Laws rueing what might have been.
He said: "After their poor performance at Lincoln last week I expected Kidderminster to come out and give us a bit of a fight.
"They did, but when we got the goal it calmed us down.
"But we began to get too cocky and extravagant and instead of going back to
simple football we tried to over-play.
"It's a game we should have won but two defensive mistakes have cost us dearly.
"We had the lions' share of the football but that's probably our worst defensive display this year."
His opposite number Jan Molby was understandably more upbeat after securing three much-needed points, but still reckoned the Iron were the best team hsi side had come up against this term.
He declared: "It was a hell of an afternoon, and the most excitement we have seen for a long long time.
"Scunthorpe are an excellent side and the best team I have seen in this League all season so to beat them under the circumstances was great.
"We only had 14 fit players to choose from and I had two injured players on the bench to make up the numbers.
"All I did was to ask them to compete and give everything they had. It was a good result and a decent performance.
"The result has given everyone a lift and the dressing room is bouncing. To be off the bottom is psychologically important and a win against a very good side can only give you confidence."