But it was a real sickener for in-form Leicester City who had dominated much of the game.
Unbeaten on their travels for five games, City looked set for a third successive away win when striker Martyn Waghorn, on loan from Sunderland, got them off to a flying start when he raced through a pedestrian home defence after just three minutes to net his fourth goal of the season.
Only some good work by goalkeeper Joe Murphy kept the home side in the game as Leicester dominated with Waghorn and Matty Fryatt a real handful up front.
Murphy reacted brilliantly to turn away a deflected shot from Fryatt and did well again to beat away a bullet header from Frenchman Yann Kermorgant.
In response, Scunthorpe were unable to muster a shot on target to trouble Chris Weale in the City goal.
United did come more into the game in the second half but twin strikers Paul Hayes and Gary Hooper were given little room by a Leicester defence in which Wayne Brown was the dominant figure.
As Scunthorpe searched for an equaliser, the closest they came was a free-kick from Grant McCann which was easily saved by Weale.
But deep into stoppage time, Woolford struck with a dramatic equaliser, drilling a shot low past Weale after City had failed to deal with a high ball into their box.