Ryan Clarke's late penalty save handed Oxford victory over Barnet to keep them in the League Two play-off places.
Michael Hector's low drive from 25 yards gave the visitors the lead, but the U's soon took control.
Scott Rendell headed the equaliser from Lee Holmes' left-wing cross before James Constable slammed in a second-half winner.
Clarke then pulled off a superb save to deny Izale McLeod from the spot after Damian Batt had tripped Ricky Holmes.
VIEWS FROM THE DRESSING ROOMS
Oxford United manager Chris Wilder told BBC Radio Oxford:
"We had to dig ourselves out of a hole as I thought the first goal was a little bit unfortunate from our point of view.
"But I thought we got ourselves back into it, started winning a few tackles, headers, got the ball wide and we started to cause them a few problems. We were dominant going into half-time and deserved the equaliser.
"They were hanging on at half-time and I think they were hanging on in the second half. We got the deserved goal to go in front and should have kicked on from there.
"They went for it at the end and we were indebted to our keeper Ryan Clarke for making a good late penalty save."