After an early delay when the floodlights failed, Elliot Osborne broke the deadlock in first-half stoppage time, converting the rebound after Chris Conn-Clark's shot was saved by Marcus Dewhurst.
Two goals inside three second-half minutes turned the game on its head with Jacob Butterfield side-footing in an equaliser in the 65th minute for United's first goal in four matches.
Scunthorpe, who went into the game on a six-match losing streak, then took the lead when Joe Nuttall made no mistake from the penalty spot after Alfie Beestin was upended.
However, former Iron winger Ryan Colclough scored a late equaliser from close range to restore parity.
Nelson said: "In the first half I felt we started well. Straight from kick-off we played through them, got a corner up at the far end, but then the lights went out, and it was really disappointing to concede a goal just before half-time.
"A few words were said at the break and credit to the lads because they came out and reacted really well in the second half. I thought we kept the ball well, having some territory and good pressure, and we started to flip it around.
"It was really disappointing we couldn't hang on in the end to keep all three points.
"Alfie Beestin and Liam Feeney made a different when they came on and it helped spin the game on its head, and we went 2-1 up. We could see them getting the ball down our left hand side so we brought Mase on to get a bit more security down there, but unfortunately we couldn't keep them out.
"It's a step forward and a point on the board away from home. We'll take this point and it will become a very good one if we can go and get all three against York at home on Saturday."
He added: "It would have been very easy for the lads to concede that goal just before half-time, and then roll over in the second half with the way things have been going lately but full credit to the lads to standing up to it."
Talking about a knock picked up by Australian full-back Reagan Ogle in the game, he added: "Reagan just picked up a touch of cramp. He does a lot of high intensity, high speed running when he plays, and has obviously been out for a little while, so it just caught up with him. Hopefully it'll settle down over the next 24 hours and he'll be fine for the weekend."
It was also confirmed after the game that Colin Daniel missed out through tendonitis which he reported at the end of training on Monday.
Nelson, who has been in position for almost a fortnight now, concluded: "I've really enjoyed being on the training pitch with an honest, hard-working group that has quality in there as well. They've been down recently and there's been negativity but hopefully we can take the positives from this. There's still a lot of work to be done, don't get me wrong, but hopefully this is a platform to work from and we can improve over the coming weeks."
See more from Michael Nelson and Jacob Butterfield on Iron Player.