Matthew Green and Ashley Barnes earned Oxford a win at Kidderminster in an ill-tempered affair which saw both sides reduced to 10 men.
Harriers' James Constable was shown the red card for an elbow against James Clarke around the half-hour mark.
Oxford's Carl Pettefer was then sent off for serious foul play.
But Green slotted home in the 30th minute and Barnes headed in another midway through the second half to seal the win for the visitors.
Kidderminster: Bevan, Bignot (Barnes-Homer 46), Creighton, Whitehead, Blackwood, Penn, Hurren (McGrath 16), Ferrell, Russell, Richards, Constable, McGrath (Christie 72).
Subs Not Used: Coleman, Smikle.
Sent Off: Constable (33).
Booked: Whitehead, Ferrell.
Oxford Utd: Turley, Clarke, Quinn, Foster, Jeannin, Anaclet (Willmott 80), Hutchinson, Pettefer, Trainer, Odubade (Barnes 51), Green (Twigg 58).
Subs Not Used: Warrell, Ledgister.
Sent Off: Pettefer (44).
Goals: Green 31, Barnes 69.
Ref: O Langford (Darlaston).