With Alex Babos sent off at the end of a goalless first half, the Bulls struggled to make an impact.
An 88th minute goal from Josh Ashby gave the visitors the lead as they took advantage of a poor clearance, but a late gamble from Paul Caddis as he brought Andy Williams and Adam Rooney on, alongside Yusifu Ceesay, failed to turn the game around.
Instead, Oxford scored a second in injury time thanks to Josh Parker. Another poor game at home.
Full report, pictures and reaction to follow.