Nicky Wroe's spectacular 87th-minute strike finally saw off the ten-man hosts, to the delight of more than 1,800 away fans who had made the short trip to Adams Park.
The win kept the U's in touch with Sky Bet League Two's leading pack and provided a confidence boost ahead of Tuesday night's FA Cup third round replay against Charlton Athletic at the Kassam Stadium.
Watch highlights of the victory here:
Plus reaction from Wroe, manager Chris Wilder and full back David Hunt:
Both videos come via Oxford United's Youtube channel.