Kilmarnock had not tasted defeat at Tannadice Park since 1997, but it was unlucky thirteen this time.
Having not lost there in the last 12 games, the Ayrshire men were put through the mill.
After intense pressure from the kick-off, the Tangerines opened the scoring in the 11th minute. After a harsh tackle by Garry Hay on the right flank, Barry Robson curled in an inviting cross for Jim McIntyre to beat Colin Meldrum and head in off the bar.
United continued to drive forward with some superb fluent passing putting Killie all over the place and it was no surprise that they doubled their lead in the 21st minute.
Alan Archibald's high ball was knocked down by Andy McLaren for Charlie Miller to calmly volley home from 12 yards.
With United's keeper, Paul Gallacher, almost a spectator to the game, United made it three in the 26th minute. Robson took advantage of David Lilley's indecisiveness and ran towards goal, stabbing the ball to McIntyre.
The ex-Killie striker curled the ball high into the net from 14 yards.
The one-way traffic continued and Miller should have made it four before McIntyre completed his hat-trick in the 34th minute.
Derek McInnes dribbled into the box and passed it for the in-form striker to smash the ball high in off the keeper's near post from eight yards.
As United's midfield continue in full throttle the Ayrshire men found some respite when the referee blew for the half-time whistle.
After the goal rush of the first period from the Tangerines, Kilmarnock grabbed small consolation with a goal from Danny Invincibile in the 61st minute.
Kris Boyd surprisingly beat Chris Innes in the air to nod the ball down for the Australian to drive the ball past Gallacher.
But the day however belonged to United.