A 55th minute lobbed winner from Jack Midson was enough to send Yeovil Town tumbling out of the FA Cup at the first hurdle at a cold Kassam Stadium this afternoon.
Midson's effort capped a battling performance from the home side who deservedly take their place in the second round draw.
The Glovers went into the match missing keeper Alex McCarthy, refused permission by his parent club Reading to play.
Richard Martin deputised while Ben Roberts joined a youthful looking bench that included youth players Rob Clowes and Rhys Baggridge along with returning striker Dean Bowditch, absent since the first game of the season.
The first quarter of the game saw the League One side looking comfortable, forcing a fourth minute corner. Andy Welsh crossed deep but Craig Alcock couldn't keep his header on target.
Midson was in action early when he got on the end of a deep Damian Batt cross but also couldn't get his effort goalwards.
United came back into it more and keeper Martin made a brave block from a Matt Green shot on eleven minutes and Green went looking for a penalty two minutes later but referee Cook didn't fall for his theatrical tumble in the box.
Welsh had the Glovers first sight of goal but his right foot shot soared over the bar.
Referee Cook got his book out for the first time when Batt went in very late on Nathan Jones flattening the Glovers assistant manager in the process.
Halfway through the first half, the home side fought their way back into the match territorially and the move ended with Green back-heading his chance over.
Yeovil midfielder Ryan Mason, impressive in the centre of the park as ever, fired a shot straight at keeper Ryan Clarke on the half hour .
Sam Williams earned a talking to from the official for going in late on Oxford's Steven Kinniburgh but escaped a booking.
Jon Obika created his first chance but saw his attempt blocked and Mason again saw Clarke deny him getting down low.
The end of the first half ended with Terrell Forbes yellow-carded for bringing down bustling striker James Constable and Midson booked for hacking down Welsh in full flight.
Mason started the second period keen to make an impression and again tested Clarke from long range but received a yellow for his late challenge on Dannie Bulman.
Oxford were coming more into the game and forced their first corner on 51 minutes but three minutes later saw their pressure pay off when Midson lobbed keeper Martin and saw the ball drop into the net.
Manager Terry Skiverton immediately shuffled his back bringing off Jones and replacing him with Danny Hutchins.
Steven Caulker had to be smart to clear as Constable was ready to pounce as the hosts kept pushing forward.
As Yeovil tried to impress, Mason shot way over when he was set up by Keiran Murtagh.
Welsh was withdrawn for George O'Callaghan on the hour and Murtagh saw yellow for fouling full-back Batt.
The huffing and puffing increased as the Glovers became increasingly desperate for an equaliser. Obika glanced a Hutchins cross wide after Shaun MacDonald's shot was blocked .
The Welsh midfielder saw his 30-yard scuttling effort dealt easily with by Clarke on 82 minutes but in truth, the Glovers were still looking toothless in attack.
Four minutes of stoppage time were announced and Obika's shot was smothered by Clarke but it was too little, too late for the Glovers who have now exited the first round four years in a row