James Constable's winner was enough to see off Dagenham & Redbridge and enhance Oxford's play-off hopes.
Oli Johnson opened the scoring for the U's, deftly heading home Liam Davis's left-wing cross.
The visitors equalised through defender Mark Arber, who planted a header across goal and past keeper Ryan Clarke from Medy Elito's flighted cross.
The game looked to be heading for a draw, before Constable's fine finish sealed the points for the home side.
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Oxford United manager Chris Wilder told BBC Radio Oxford:
"I'm not loving the performance but you've got to give the players a far bit of leeway.
"It was a tight game but we took our chances, we should have scored a few more, and had an added spark after the break.
"There have been plenty of occasions this season when we haven't got what we deserved so it was nice to get the victory. Hopefully this will boost us and we can go on a bit of run in terms of winning games of football.
"The main focus was to go and get a win and we did that."