In-form Plymouth extended their run to just one defeat in 14 League One games with a 1-0 victory at Oxford.Centre-half Sonny Bradley struck in first-half stoppage time when he met Graham Carey's corner with a powerful header from beyond the far post to claim all three points.It was a third-straight defeat for managerless Oxford, yet the U's were positive and purposeful in the first half.James Henry saw his deflected shot beaten out by Argyle goalkeeper Remi Matthews, and Alex Mowatt hit a half-volley over from eight yards from Todd Kane's cross.In the end-to-end contest, Carey got behind the home defence but his scooped shot drifted wide.Oxford suffered a blow when they lost midfielder Joe Rothwell to injury before the break.Argyle almost made it two when Ryan Taylor shot against the top of the crossbar and again when Carey's effort was cleared off the line by Todd Kane.Gino Van Kessell gave United more urgency when he came off the bench but the Pilgrims defended well - with some vital blocks - to keep a clean sheet.