Mangotsfield United went into this game knowing that a win would secure a place in the Cossham Street history books as no other side had progressed beyond the final qualifying round.
After a scrappy opening ten minutes Mangotsfield drew first blood going ahead in the 12th minute after Danny Carter's ball in from the left was brought down by Liam Monelle whose well struck volley found the back of the net despite the best efforts of the Oxford keeper.
Just two minutes later Jamar Collins drove down the left wing working the ball inside to George Cryer who in turn laid it off for Monelle to extend Mangotsfield's early lead.
Despite making an ideal start Mangotsfield had to soak up a good deal of pressure, goalkeeper Ollie Player twice being called upon to deny the visitors.
Joe Thomas had the best chance of the remaining time in the first half as his dipping shot just skimmed the crossbar.
The second half saw Oxford press hard for in a bid to reduce the deficit as Mangotsfield relied on the counter attack. Oxford were rewarded with a goal on 65 minutes, Ollie Player saving only for the ball to be forced home after a goalmouth scramble as Mangotsfield finally succumbed.
George Twose came on in replace of George Cryer to sure up the midfield leaving Liam Monelle as a loan striker. A second change for Mangotsfield saw Will Harrison replace Grant Ogborne in the 72nd minute.
Mangotsfield's two goal lead was restored after Joe Thomas won the ball deep inside his own half making 50 yards before releasing Monelle who beat the offside trap to slot the ball home for Mangotsfield's third and Monelle's hat trick.
The two goal cushion lasted a matter of minutes as another Oxford attack ended with a penalty being awarded after the visitors striker was brought down by Ollie Player.
The remaining 12 minutes proved to be nerve racking but the Mangotsfield rearguard stood firm to book a place in the first round proper for the first time in the clubs history.
*In the first round proper Mangotsfield United travel to Cirencester Town on Thursday 1st November kick off 7.30pm. Admission charges are £5.00 adults and £3.00 Concessions.
Mangotsfield United: 1. Ollie Player, 2. Mayson Evans, 6. Craig Baptist, 14. Harry Madge, 20. Josh Bennett, 4. Danny Carter, 12. Grant Ogborne (72', 19. Will Harrison), 11. Jamar Collins, 7. Liam Monelle, 18. George Cryer (68', 15. George Twose), 10. Joe Thomas.
Substitutes: 17. Tom Booth, 5. Harry Iles, 19. Will Harrison, 15. George Twose.