Chris Wilder recorded his first Blades win - against his old club.
Kane Hemmings gave Oxford a first half lead but Billy Sharp levelled and James Wilson powerfully headed his first goal for the club to win it.
Chief Wilder made two changes; Wright made his debut against his former club and Done also started. O'Connell and Clarke, who missed training with injury in the week, dropped to the bench. Fleck also returned to the bench.
Basham picked up a booking inside a minute for a late sliding challenge on Dunkley, whilst the early momentum and chances dropped to the visitors. Moore saved comfortably from Maguire and then the Oxford striker slid the ball into the side-netting from a Hemmings cross on 13 minutes.
Oxford, however, grabbed the lead on 16 minutes from a free-kick, conceded by Wright, who picked up a booking in the process. A short free-kick saw Sercombe given the space to shoot from 30 yards and after Moore's parry, HEMMINGS was the first to react to slot over the sprawling home goalkeeper.
The Blades responded with a spell of pressure, which included a number of corners. From a Duffy free-kick, Wilson almost attached himself to the ball at the back post and Dunkley did well to block from Freeman after Done's neat ball through the defence.
As the half wore on the pressure continued to come from United. Done shot over on the turn after Wilson recycled Hussey's corner and after Scougall's pass beat the Oxford defence, Eastwood saved from Done.
However, the Blades were unable to redress the balance, leaving boss Wilder with a tough half-time team-talk, which included Hussey being replaced by O'Connell.
The opening ten minutes of the second half saw a chance at each end. From Duffy cross, Ruffels almost headed into his own net but goalkeeper Eastwood recovered to save, whilst Moore made a fine stop from Lundstram after Maguire's short free-kick.
On 64 minutes a mistake by Dunkley gave Done an opportunity but his shot was straight at Eastwood, the Blades were level soon after, though. Done found space on the left and from his cross, SHARP battled with his marker and managed to steer the ball home at the back post - before falling over an advertising hoarding at the Kop end.
Eight minutes later, with the next notable chance, the Blades went ahead. A foul by Ruffels resulted in Duffy whipping a free-kick from the right and WILSON beat Eastwood with a powerful header, again at the Kop end.
Done's endeavours were applauded by the Blades fans late on, whilst Duffy saw a lot of the ball to keep Oxford on the back foot. Clarke replaced Sharp for the final few minutes and the home side professionally saw the four minutes of added time to breath a sigh of relief.
Blades: Moore, Hussey (O'Connell 45), Basham, Scougall (Fleck 80), Sharp (Clarke 86), Done, Wright, Coutts, Freeman, Wilson, Duffy.
Unused: Ramsdale, Calvert-Lewin, Whiteman, Chapman.
Oxford: Eastwood, Skarz (Martin 45), Lundstram, Sercombe, Thomas, Maguire, MacDonald (Rothwell 73), Ruffels, Hemmings (Taylor 67), Edwards, Dunkley.
Unused: Crowley, Buchel, Roberts, Ledson.