A nervous encounter at the Vetch saw the only goal of the game come just before half time with Kris O'Leary rifling into the top corner after Oxford failed to clear thier lines.
Swansea's grip on the game was never likely to be challenged towards the end of the game as Oxford had Mateo Corbo sent off with 20 minutes remaining.
With Southend United suffering an LDV Vans Trophy final hangover, losing to Leyton Orient, tonight's result probably couldn't have worked out better for Kenny Jackett's men.
Swansea now lie level on points with Southend, but are behind on goal difference.