Wimbledon were outclassed in the first 20 minutes and outnumbered in the last 30 as leaders Oxford ran out comfortable winners in the Dons' first visit to the Kassam Stadium.

Everything about this game had the feeling of a midweek cup tie against a team from a higher division. The capacious, modern (albeit three-sided) stadium, the distance the all-seated Dons fans were from the pitch and the fact that for the first 20 minutes Oxford played like a League One side, never mind the Blue Square Premier leaders, all added to an atmosphere that the visitors had not previously encountered for a league game.

It wasn't as though Terry Brown's side, unchanged after Saturday's magnificent win at Luton, started poorly - the U's began so strongly that the Dons were in danger of being blown away within the first quarter of on hour. With Sam Deering and Chris Hargreaves pulling the strings in midfield, United peppered the Dons penalty area almost from the kick off and James Constable missed a simple header from a Deering cross with less than two minutes gone. Deering's inswinging corner not long afterwards then gave the unmarked Rhys Day the chance to put Oxford one up but he glanced his header over James Pullen's bar from six yards.

With barely another two minutes gone, Pullen pulled off a truly magnificent save when he got down low to his right to parry Simon Clist's powerful drive from the edge of the box which more than made up for his two missed punches from earlier crosses from Deering and Anthony Tonkin. The Dons weren't just at sixes and sevens, they were at tens and elevens - Ben Judge and Paul Lorraine had put as much effort into the first few minutes of this game as they had into some entire games and, forgive the cliche, it was only a matter of time before Oxford scored.

When they did, on 14 minutes when Constable converted Matt Green's flick on from 18 yards with a low drive past the motionless Pullen, it should have been an equaliser. The Dons had put together a fine flowing move, involving Glenn Poole, Steven Gregory, Nathan Elder and Lewis Taylor that saw Elder play Danny Kedwell in behind Chapman with a perfectly weighted through ball. But, from just 10 yards out and with keeper Ryan Clarke not in the greatest of positions, Kedwell's control let him down and the chance had gone.

Pullen was called into sharp action again when Deering's low cross seemed destined for Constable's toe before the Dons keeper smartly intervened, but Oxford's incisive passing and quick thinking was a class above anything the Dons had encountered this, or any other season. That said, two more decent chances came and went either side of Taylor's ankle injury that saw the AFC Wimbledon midfielder leave the action with the first half only semi-completed.

Jay Conroy came on at right back with Sam Hatton moving into midfield and Hatton's first piece of action saw his deep cross to the far post headed against the bar by the otherwise well-shackled Elder. Hatton then had a chance of his own but scuffed a 20 yarder well wide. Another Hatton cross then fell kindly for Kedwell but although his control and turn were well-executed, he fluffed the finish. Elder did likewise when Gregory's long ball over Day and Jake Wright found the big striker in behind the Oxford defence but as Clarke raced out of his box Elder was forced to rush his shot and his effort bobbled well wide.

That flurry of chances blew itself out as the first half drew to a close. With them went the Dons' only opportunities, as it turned out, to get back into the game as Oxford came back strongly in the last few minutes of the half. Deering had faded as Gregory had grown more influential but the diminutive midfielder's prodding and probing almost led to a second goal before the break, Judge's timely intervention denying Green a clear shot on goal after a deft Deering flick had bypassed Will Hendry and Lorraine.

The Dons, watched by Chris Hussey for the first time since he joined Coventry City in October, went into the break no doubt feeling quite relieved at only being a goal down but at the same time ruing those missed chances.

United started the second half in similar fashion to the first - slick passing with pace and precision outmanoeuvring the Dons defence at will, the pace of Deering and Green in particular causing all manner of problems as Wimbledon's central midfield pairing of Gregory and Hendry started sluggishly and gave Judge and Lorraine little protection. Deering seemed intent on regaining control of the game and he, Bulman and Hargreaves were starting to dominate once again and Oxford's substitute keeper Billy Turley barely touched the ball in the first 15 minutes of the half.

On the hour mark came the moment that all but ensured this was not going to be Wimbledon's day. Lorraine's clearance near the half way line was blocked by Deering and he bore down on goal. The only Dons defender able to catch him was Conroy and just as Deering entered the D, Conroy brought him down for the straightest of red cards. From the resultant free kick Pullen made another magnificent save, palming Clist's bullet to eventual safety. He did the same less than two minutes later, dealing with Green's 12 yard volley in similar fashion as Oxford seemed intent on making their numerical superiority count.

Green should have put the game beyond the Dons on 70 minutes when he broke past Danny Blanchett and shaped to shoot from 15 yards but a cute nudge from Judge unbalanced the pacy striker and he shot high and wide.

With 10 minutes left, the scoreline finally reflected the true pattern of the game. Constable's cross set up Aldershot loanee John Grant and with only his third touch as an Oxford player he forced another great save from Pullen but the rebound fell kindly for Constable and he buried his 20th goal of the season with a tidy close range finish.

As the 800 or so Dons fans filed out of the Kassam at the final whistle, they were doubtless grateful that their side's goal difference hadn't taken as much of a battering as their defence had - Oxford looked, at times, a class above Blue Square Premier level and comfortably condemned the Dons to only their second defeat by more than a one goal margin this season. This Saturday's break from Conference action is now slightly more welcome than it might have been.