Forest, having lost six of their last seven First Division games, needed a boost away from the arduous task of collecting league points.
Although they took the lead after 39 minutes through recalled striker Dougie Freedman, Forest failed to hold on to their advantage and a 76th- minute equaliser from the substitute Paul Powell took the tie back to the Manor Ground.
Oxford almost clinched victory through another sub, Jamie Cook, when he crashed his late shot against the Forest post.
It had all started so promisingly for Forest, who dominated much of the first-half play but only had Freedman's effort to show for their endeavours.
But they failed to build on their lead and suffered the almost inevitable consequences when Powell equalised with a shot from 25 yards.
Forest still might have snatched victory 11 minutes from time, but Freedman shot wide from just eight yards.
Nottingham Forest: Beasant; Hjelde, Quashie, Brennan, Doig, Prutton, Scimeca, Bart-Williams, Gray, Freedman, John. Substitutes not used: Bonalair, Harewood, Merino, Williams, Crossley (gk).
Oxford Utd: Lundin; Wetherstone, Watson, Whelan, Folland (Powell, 57), Murphy, Robinson, Beauchamp, McGowan, Anthrobus (Cook, 57), Lilley (Fear, 76). Substitutes not used: Weatherstone, Arendse (gk).
Referee: A D'Urso (Billericay).Reuse content