Ten-man Oxford extended their unbeaten run to nine in all competitions after a comfortable 3-0 win at Wimbledon.
Goals from Sean Rigg, Alfie Potter and Tom Craddock condemned the Dons to a relegation place going into the new year.
Following a spell of little action, the visitors took the lead just after the half hour, a lovely defence splitting pass from Potter found Rigg who slammed his shot into the top corner.
Soon afterwards the away side doubled their lead, Rigg turned provider this time as his cross found Potter who nodded the ball over the line.
Wimbledon had a good spell early in the second half but failed to convert their chances and United killed the game just after the hour.
AFC's Will Antwi attempted to head back towards his goalkeeper Neil Sullivan but Craddock was there to pounce and coolly slot home for his 11th of the season.
United's afternoon was soured though as James Constable was sent off for an apparent elbow on Antwi.