An early strike by winger Matty Kosylo was enough to give the Motormen all three Skrill North points at Rivacre Park on Saturday.
The goal was scored after just four minutes when a pass was played out to Kosylo on the left wing. He cut inside and drilled the ball into the corner of the net from just inside the area.
Motors could have been further ahead in the first half, with Lloyd Ellams firing inches wide on 12 minutes.
Ellams went close again on 37 minutes, weaving his way into the box and seeing a left-footed effort well saved by Oxford keeper Victor Francoz.
Just before half-time, the home side should have doubled their advantage when Tom Hannigan crossed to fellow centre-back Andy Nicholas, who somehow put the ball over the crossbar from just six yards.
Oxford rarely threatened in the final third and had to wait until the 77th minute for their first effort on goal.
Tom Winters played in a dangerous cross from the left to substitute Mike Symons, who hit a sweet left-footed effort towards goal. But keeper Zac Jones got an outstretched leg to his effort and did well to turn the ball over the crossbar to safety.
Kosylo and Louis Barnes both went close in the final stages but man-of-the- match Francoz pulled off two spectacular point-blank saves at the near post to keep the score at 1-0.
Vauxhall: Jones, Wainwright, Barnes, Hannigan, Nicholas, Noone (Clair 83), Rutter, Williams, Noon (Rugg 73), Ellams, Kosylo (Stott 90). Subs: Davies, Ellison.
Motors play Evo-Stik Premier side Chorley at home in the second qualifying round of the FA Cup on Saturday. Kick-off at Rivacre Park is 3pm. Admission: £10 adults, £6 concessions, under 16s £2.
