United dominated large chunks of the game at the Kassam Stadium, but Oxford's summer signing Tommy Mooney struck a super free-kick equalsier to gain the hosts a point.
The Iron were far sharper to the ball in an awesome first half, with Cleveland Taylor causing massive problems down the right.
Oxford boss Graham Rix was forced to field a makeshift defence because of injuries and suspension and the U's began the game with an unusual 1-2-4-3 formation with Barry Quinn operating for the first time as a sweeper.
Richard Kell, Taylor and Nathan Stanton all went close to a breakthrough goal for Scunthorpe and as the visitors ran the show, on-loan forward Andy Keogh fired just past the post after a clever link up with Paul Hayes.
Kell suffered an off the ball injury, and had to be replaced by Matthew Sparrow.
A brilliant one handed save by Oxford keeper Chris Tardif denied Paul Hayes when he struck a super volley, but Scunthorpe took the lead moments later. A long punt forward by Andrew Crosby was misjudged by Jon Ashton and Paul Hayes raced forward 30 yards and rifled in a low drive.
While the Iron had dominated the first period, Oxford were a different side in the second half.
Robert Wolleaston was unlucky not to level when he showed great control to beat his marker only to have his fierce shot beaten out by Paul Musselwhite.
Mooney made it 1-1 nine minutes into the second half after a free kick awarded for a foul on Julian Alsop. Mooney's drive deflected off Peter Beagrie in the wall and arrowed into the top corner.
Scunthorpe felt they should ohave had a penalty just before the end when Taylor looked to be upended in the box by Matthew Robinson, who was already on a yellow card but the referee ignored their appeals.
And former Oxford skipper Andrew Crosby was within a foot of grabbing the winner back on his old stomping ground when he glanced a corner just wide from four yards with just eight minutes to go.