United took the lead in 14 minutes when David Robertson headed home and doubled their advantage three minutes before the break when David Goodwillie chipped Greg Kelly after a long ball out of defence. Two minutes later Robertson added number three with a shot from twenty yards.
Thirteen minutes after the restart, Chris Maguire won a penalty when he was brought down in the box only for his resultant spot kick to be saved. The youngster made amends seven minutes later when a long Kelly clearance was fired home to make it 3-1.
However there was more misery for Aberdeen in the 75th minute when Dan Smith, who had already been booked, was sent off for a last man challenge. Willie Easton took the free kick giving Kelly no chance to complete the scoring.