It was the hosts who started the better not unexpectedly with confidence high. After a James Grady flick which went narrowly wide, Chris Clark tried to lift the Dons with a blistering 50-yard drive in the sixth minute. This worked for the Dons as they scored in the ninth minute courtesy of some poor defending.
A curling free-kick was missed by two United defenders giving Alexander Diamond an easy shot to fire home from ten yards.
The Tangerines, stunned by this, tried to push the Dons back.
Diamond was rather fortunate not to give away a penalty in the 27th minute before Grady smacked an edge of the box shot which skimmed past post.
Despite United's continuous pressure, against the run of play Aberdeen made it 2-0 on the stroke of half-time. Again the United defence couldn't clear a corner and the ball fell to substitute John Stewart who rattled in a 12-yard deflected shot past the wrong-footed keeper.
The second half saw United completely dominate, opening with a clear opportunity for Stevie Crawford, but unfortunately he mistimed his touch when it seemed easier to score.
The Tangerines were given some hope in the 55th minute when Diamond was given his marching orders for his second yellow card. Having brought down Jason Scotland in the first half, he foolishly wrapped his legs around Barry Robson giving the referee no option.
Eventually United pulled one back in the 60th minute with a deserved goal for the hardworking Scotland. Mark Kerr won the ball at the edge of the box and fed the striker who coolly slipped the ball home from 12 yards.
The remainder of the match saw Aberdeen survive a number of scares and United's frustration came to a head two minutes from time.
Referee Craig Thompson, who had had a poor display throughout, pulled out his red card for the second time judging Paul Ritchie to have pulled down Darren Mackie to earn himself a second yellow card.