IT WAS a show of unbridled delirium at a job almost well done.

As a vision of beach balls, flags, scarves and bouncing Aberdonians provided a colourful backdrop to this mesmerising contest, it was the unlikely figure of Scott Vernon who emerged to the foreground to almost single-handedly haul Aberdeen to within touching distance of their highest finish in a generation.

Drafted in to the starting XI due to an ankle knock sustained by Adam Rooney at the weekend, the 30-year-old striker's hat trick, the goals all coming at crucial junctures, put Derek McInnes' men four points clear of Motherwell in second place in the SPFL Premiership, with the Lanarkshire club now needing to beat Inverness Caledonian Thistle tonight before turning over Aberdeen at Pittodrie in one of the most exciting matches both will play for some time.

It will need to go some way to top this affair, though. Despite holding much of the possession and having by far the more clear-cut chances, United were undone by a mixture of good finishing, ridiculous defending and bad luck as their hopes of achieving a Europa League spot through league placing was dashed.

The Tannadice club will now look to their William Hill Scottish Cup final for a return to continental football while Aberdeen look forward.

"It was a brilliant win for us," said McInnes. "The contributions from Jamie Langfield and Scott Vernon were pivotal. We easily could have rolled over in the second half but we did not. We expect we have to go and get a result on Sunday and not look to depend on other people."

It took only seven minutes for Vernon's selection - the only change for Aberdeen - to be validated. Peter Pawlett cut in from the right side towards the United box; his heavy touch was taken in his stride by his fellow forward, who darting away from goal showed great composure and balance to roll the ball to his left and under the collapsing figure of United goalkeeper Marc McCallum.

It took the influence, or its absence, of a former United man for the home side to gain a foothold in the match. After half an hour Willo Flood pulled up just inside his own half, leading to the hobbling 29-year-old being replaced by Cammy Smith.

Within four minutes United were level. Nadir Ciftci collected the ball on the left before swinging a high and heavy cross to the back post. Stuart Armstrong brought the ball down effortlessly on the far side, affording the midfielder time to play a perfect reverse pass to the in-rushing Sean Dillon, who took the ball beyond one defender with his first touch, and beyond Jamie Langfield with his second, a fierce shot appearing to take a nick on its way in.

It proved to be the catalyst for a sustained period of United pressure which should really have seen the game put out of reach of Aberdeen. Before the break Andrew Robertson ghosted into the box to launch a fierce left-foot volley at goal with Langfield throwing himself low to his left to parry, with Wilson's goalbound half volley being tipped on to the bar moments later from 15 yards. Seconds after the restart, Andrew Robertson's drilled cross was practically taken off the toe of Brian Graham at the back post by Jonny Hayes, with the United forward appearing to be hauled to the ground by Russell Anderson in the box seven minutes later.

This was to become a period of regret for United, who were punished ruthlessly by their visitors. Just seconds after McCallum had blocked a Vernon shot from point-blank range, he was more than questionable at the resulting corner.

Barry Robson's whipped delivery should have been attacked by the 21-year-old goalkeeper, instead he stood flinching on his line, allowing Vernon to meet it powerfully with his head from five yards. If McCallum was suspect for the second, Gavin Gunning was guilty as sin for the third, killing off any hope United had of catching Motherwell in third place.

A high ball was tossed in the centre-half's direction, only for him to completely miss a glancing backwards header to his goalkeeper, with Vernon ghosting in to collect, rounding McCallum and slotting through the legs of John Souttar on the line.

It was a result which flattered Aberdeen while exacerbating Jackie McNamara, the United manager. Not only did he also witness Nadir Ciftci blaze high over unmarked just seconds after going 2-1 behind, he also had to deal with Ryan Dow having a seemingly legitimate goal disallowed seconds later.

"I don't think we deserved to lose, but if you make mistakes like that they can be costly," said McNamara. "All three goals were preventable."