Sam Long and Olamide Shodipo struck from the bench to lift Oxford off the foot of the League One table with a 3-2 win over MK Dons.
Long replaced the injured Rob Atkinson at centre half on 54 minutes and, just four minutes after arriving on the pitch, he powerfully headed in Anthony Forde's free kick.
And Shodipo, on loan from QPR, struck with his first touch, his long-range effort a minute from time going in off a post.
It brought the U's their first home win of the season, and sends them into the weekend's big local derby against Swindon in better spirits.
United had been given the perfect start with Matty Taylor turning in Marcus McGuane's low left-wing cross from close range on six minutes.
But Dons were level five minutes later as Cameron Jerome fired in Dan Harvie's pinpoint cross.
The visitors looked threatening going forward and would have been disappointed not to have been ahead by half time.
Yet it was Oxford who ran the second half, before Ben Gladwin pulled a second goal back for the Dons with a 20-yard shot in stoppage time.