Tom Hopper and Anthony Scully were on target as City recorded their first league win of the season, stretching their unbeaten start to the campaign to five matches in the process.
Both City's goals came in the first half as Mark Kennedy's side turned on the style, with Cameron Brannagan pulling one back for the hosts after the break.
Karl Robinson's men pushed for a leveller, but the Imps dug deep and battled hard in the Oxfordshire rain to ensure three points.
The visitors had the first effort at goal as Max Sanders drove into Oxford’s penalty area from the left before striking straight down the middle into Simon Eastwood’s grasp.
The hosts responded with a spell of pressure which saw Billy Bodin aim a cross towards Matty Taylor in the centre, but a City defender rose highest to flick the ball away to safety.
Jordan Wright was called into action shortly after when Lasse Soresen sliced Bodin’s cross into the gloves of the goalkeeper, who was making his first appearance of the season.
Robinson’s side continued to show intent during the opening stages and went close again when Browne found Bodin in space in the left side of the area, but he could only drag his shot wide of the near post.
The deadlock was broken in the 21st minute as Garrick played the ball out to Scully on the left who crossed in for an unmarked Hopper to head down past Eastwood and into the net.
City looked the stronger side after taking the lead but it was Oxford who had the next best chance of the evening after they broke away to allow Brannagan to rifle his attempt just wide of the post from 20 yards out.
Kennedy’s side doubled their advantage on the stroke of half-time when Sanders won the ball on the edge of the box before playing Scully in, with the City forward bending his effort into a corner of the net to score his first league goal of the season.
Oxford began the second period on the front foot and almost pulled one back as Brannagan managed to get away from Regan Poole’s tackle to force Wright into a smart stop at his near post.
The hosts continued to try and find a way back into the contest when Sam Long whipped in a teasing cross towards Bodin on the hour mark, but the winger failed to direct his effort on target.
Moments later the Yellows were awarded a free-kick in a good position which was struck over the wall and into the side netting by Browne.
Oxford were handed a way back into the match after the referee pointed to the spot when Sanders pulled down Kyle Joseph inside the box.
Brannagan stepped up for the resulting spot kick and slotted it into the bottom right corner to reduce the arrears.
City stood strong to the resulting pressure that followed as Jamie Robson headed James Henry’s goalbound effort over shortly before Paudie O’Connor knocked an inviting cross clear - ensuring the Imps collected their first three points of the campaign.
Oxford: Simon Eastwood, Sam Long, Stuart Findlay, Elliott Moore ©, Billy Bodin (Kyle Joseph 60’, Cameron Brannagan, Matty Taylor, Marcus Browne (Tyler Goodrham 67’), Lewis Bate (James Henry 57’), Marcus McGuane, Steve Seddon (Ciaron Brown 67’). Subs (not used): Ed McGinty, Alex Gorrin, Jodi Jones.
Goals: Brannagan (69’ pen).
Imps: Jordan Wright, Regan Poole, Max Sanders, Tom Hopper ©, Anthony Scully (Sean Roughan 72’), Jordan Garrick (Charley Kendall 82’), Paudie O’Connor, Jamie Robson, Ben House (Tashan Oakley-Boothe 55’), Lasse Sorensen, TJ Eyoma. Subs (not used): Charles Vernam, Ted Bishop, Chris Maguire, Sam Green.
Goals: Hopper (21’), Scully (45+2’).
Referee: Samuel Barrott
Attendance: 6,912 (326 away).
