OXFORD United’s 18-game unbeaten run was brought to an end as Joe Mason’s strike settled a dour game in Milton Keynes Dons’ favour.

The visitors, backed by almost 3,000 supporters, lacked a spark for the second game running and were unusually passive in the first half.

The Dons, who remain in the Sky Bet League One relegation zone despite the result, were not much better and took almost an hour to muster the contest’s first shot on target.

It was good enough to claim maximum points, though, as Mason fired in from 12 yards.

United showed more urgency after falling behind, but despite some late pressure were unable to carve out a clear chance.

It meant a first defeat since September 7 for Karl Robinson’s side, who now turn their attention to Manchester City in the Carabao Cup quarter-finals on Wednesday night.

The teamsheet brought a surprise with the return of Cameron Brannagan after seven weeks out, while Alex Gorrin returned from suspension.

United’s big support chanted in tribute to Jim Smith from kick-off and the visitors threatened within seconds as Chris Cadden’s cross forced a corner.

When it was played short to Brannagan, his left-footed cross almost fell for Rob Dickie before the hosts cleared.

That was about as threatening as United were in an otherwise sterile first half.

They sat off the Dons, who moved the ball at a slow tempo, which made for a drab spectacle.

If the tactic was designed to lure the hosts forward so they could be attacked on the break it failed, partly because when United won it back their play was full of errors which prevented them from building any momentum.

The initiative was with the Dons, but they lacked quality around the box.

Jordan Archer was almost as much of a spectator as Lee Nicholls at the other end. Mason came closest with two shots from 20 yards, but both missed the target.

The half was summed up in its final seconds, when Gorrin gave away a free-kick in a dangerous area, but Dean Lewington’s effort sailed well over into the empty seats between the two sections of away fans.

United pressed higher after the break and played Fosu through the middle, but they still lacked sharpness.

The game meandered along until the deadlock was broken just before the hour mark.

It took a slice of fortune, as Hiram Boateng’s shot from the right was deflected into Mason’s path, but from then on he took the chance well. A quick change of direction got him away from Ruffels and into space for a rising shot past Archer.

United, who had brought on Jamie Mackie just before the goal, were immediately more expansive after falling behind.

The bumper travelling contingent roared their encouragement as Cadden got into a couple of promising positions.

It came to nothing, as did a penalty shout for handball when a Brannagan shot was blocked.

Dons had chances on the break as United committed men forward, Gilbey firing wide at the end of one counter-attack when he should have done better.

Substitute David Kasumu broke through in stoppage time, but Shandon Baptiste got away with a nudge in the box which saw him lose his footing.

It did not matter, though, as United fell short.

MK Dons (4-3-3): Nicholls, Brittain, Poole, Walsh, Lewington, Houghton, McGrandles (Kasumu 90), Gilbey, Agard (Bowery 83), Boateng (Reeves 71), Mason.

Unused subs: Moore, Healey, Dickenson, Sorinola.

Booked: Houghton, Nicholls, Lewington, Agard, Reeves.

Oxford Utd (4-3-3): Archer, Cadden, Dickie, Mousinho, Ruffels, Gorrin, Sykes (Baptiste 64), Brannagan (Agyei 79), Hall (Mackie 59), Taylor, Fosu.

Unused subs: Stevens, Long, Moore, Jones.

Booked: Dickie, Fosu, Gorrin.

Referee: Trevor Kettle (Rutland).

Attendance: 10,031 (2,850 visitors).