It was a game in which the Terrors had the last laugh after they had on-loan midfielder Willo Flood given his marching orders on the stroke of half-time.
But if there is one strength that Craig Levein has instilled in his side it is the desire to fight and in the end they justified their win.
As expected the game began with great effort from both teams but little enterprise to match the enthusiasm.
The visitors carved out the only chance of the opening quarter when ex-United man Lee Miller chipped the ball over Christian Kalvenes and volleyed across goal from an acute angle.
United appeared to suffer a setback, losing Steven Robb to injury, but ironically it seemed to work in their favour as they began to take a grip on the game after the arrival of sub Craig Conway.
Shaun Dillon's cross in the 26th minute created panic in the Dons defence and then a Conway cross from the other flank saw Noel Hunt nod the ball on to David Robertson whose header was cleared by the immaculate Scott Severin.
After Severin had cleared Hunt's flick off the line a few minutes later, only a magnificent stop in the top corner prevented United from taking the lead. Conway's cross was headed on by Robertson from 12 yards and somehow Derek Soutar clawed it away.
There was controversy three minutes before the break when Flood was red-carded for his second bookable offence. Having been yellow carded ten minutes earlier for a foul, the Irishman received a second caution for simulation - a decision questioned by manager Levein after the game.
With the advantage of an extra man, Aberdeen were expected to take control. A truly wonderful save from Grzegorz Szamotulski, matching the earlier stop from Soutar, frustrated Barry Nicholson in the 51st minute. The keeper flung himself to palm the ball onto the bar and away.
But gradually United edged their way back into the game. Aberdeen rode their luck in the 71st minute when Barry Robson took advantage of a defensive slip but he struck the post when he possibly should have squared the ball to Hunt.
United then created several more chances before the calamitous ending for Andy Considine. The Scotland Under-20 World Cup defender chested down Hunt's cross into the path of Robertson for the midfielder to smash the ball into the net on the stroke of full time.