United opened strongly, dominating the first 15 minutes without creating too many chances.
Forest's David McGoldrick was denied in the opening minutes by a good save from Scunthorpe keeper Josh Lillis before Joe Garner picked his way easily through the home defence in the 16th minute to find the bottom corner of the net from 12-yards.
The goal seemed to knock the belief out of the Iron, who did not create another meaningful effort before the half-time interval.
George Boyd made it 2-0 after 41 minutes with an excellent finish from the edge of the box after a good passing move had again opened up the Scunthorpe defence.
McGoldrick might have made it 3-0 when he blazed wide after a cross-cum-shot from full-back Joel Lynch had clipped the far post.
Scunthorpe battled back early in the second half when teenage centre-back Niall Canavan forced the ball home from close-range after Forest had failed to clear from a corner. Canavan is expected to sign a contract extension this week, and this was his first goal for the club.
Striker Gary Hooper had a shot cleared off the line from another corner before the visitors, who had made eight changes from the previous week, regained their composure.
The Reds had an escape in the 76th minute when Hooper, needing a goal to have a share in this season's Championship golden boot award, flicked a close-range header against the bar, to be denied his 20th goal of the campaign.
United salvaged a point when Garry Thompson, pushed up front for the final 10 minutes in place of Paul Hayes, rifled home a blistering drive from 25-yards into the top corner giving keeper Paul Smith no chance.