Matty Taylor and James Henry fired Oxford to a third successive win, as they eased past recent bogey side Accrington 3-0.
Stanley had won on their previous two visits to the Kassam Stadium but United sent them packing this time with a confident display, closing the gap on the Sky Bet League One play-off pack.
Henry gave the hosts the lead, shooting into the bottom corner from Marcus Browne's left-wing cross in the 13th minute - his 13th goal of the season.
Taylor turned the ball in at the far post five minutes into the second half when Cameron Brannagan picked him out with a chipped centre from the left.
And in-form Taylor bagged his 15th of the campaign, and his sixth goal in the last five games, by heading in Henry's perfect cross on 72 minutes.
Oxford were dominant but Accrington had their chances.
Simon Eastwood saved from Jordan Clark's header after half an hour, with Joey Pritchard's follow-up drive then blocked on the line by George Thorne.