Bolton arrived at the Kassam Stadium with the possibility of going fifth in League One after Peterborough lost 2-0 to Cambridge in the early kick-off.
That result put added pressure on Oxford who sit level on points with Cambridge, with the Yellows sitting just above the relegation zone on goal difference.
Team news
Captain Elliot Moore came back into the team this afternoon following a game out with concussion.
Brandon Flemming started at left wing with Josh Murphy on the right, who kept his place in the side following calls for youngster Tyler Goodrham to get his first minutes under new boss Liam Manning.
For Bolton, Kyle Dempsey started following a suspended sentence earlier in the week. The midfielder was involved in an assault incident in the summer, but was released this week.
Early goal the difference
Bolton took the lead six minutes into the game. A fortunate break for the away side found Dion Charles 12 yards out. U's keeper Simon Eastwood was too eager to intercept the cross and a simple pass into the open net gave the visitors the lead.
As the half grew old, United struggled to develop a rhythm in the game as both sides were limited to half chances.
Josh Murphy's cross from the right hand side found the head of Stuart Findlay in acres of space who couldn't connect from six yards out in a passage of play that seemed to sum up United's season.
37 minutes into the game and Oxford felt they should've had a penalty. Kyle Joseph was played in behind the Wanderers back line, and poked the ball past the onrushing James Trafford, who had come storming out of his penalty area.
Trafford took out Joseph, only to be brandished with a yellow card by referee Sebastian Stockbridge, much to the despair of the Oxford faithful.
United grew into the game in the last 10 minutes of the first half, getting more success from infiltrating the Bolton back line and the space in behind it.
More chances were created, however the corners and free kicks won from those passages of play lead to nothing.
United started the better of the two teams in the second half. Tyler Goodrham came on for Josh Murphy, much to the delight of the home fans.
The Yellows were playing with more intensity, Sam Long was linking up well with Goodrham down the right hand side.
53 minutes in and United should've been level. Goodrham flicked the ball through two Bolton players to Long, whose cross found Joseph who couldn't connect properly.
The pressure continued to grow on the Bolton goal, with United applying more and more pressure. Goodrham again found space to get a cross in but Joseph couldn't get enough power on it.
Bolton were struggling to cope with the high press, and gifted United the ball in the area, but the home side couldn't work an opening from 16 yards out.
The away side then gave a reminder of why they are in the play-offs. A quick attack with interchangeable football down the right hand side found Kyle Dempsey free on the edge of the box but shot just over the bar.
United pushed on as the minutes ticked by, but Bolton stood strong.
The chances began to dry up for the home side as they grew more and more desperate for an equaliser.
Bolton managed the game well, spurred on by the away support.
As the clock ticked down, Oxford looked to force an opening. Cameron Brannagan, who has been United's talisman this season, twisted and turned all he could but could not create an opening.
As the final whistle sounded, a chorus of boos could be heard from the home ends, more about the referee than anything.
The game finished 1-0 to Bolton, which saw the away side move up to fifth in the league.
United stay one place above the drop zone in 20th, not for the lack of trying this afternoon. The home side were applauded of by their home fans, who saw a very different and impressive second half.
Attendance: 9,506
Referee: Sebastian Stockbridge