Kilmarnock's blistering first-half display tore United apart as Kris Boyd became the first Killie player for 15 years to score five goals in a match.
The visitors had no answer to Boyd's power and the pace of Danny Invincibile and Craig Dargo.
Peter Leven took over from Eric Joly in the heart of midfield and will surely be rewarded with a new long-term contract after a superb display, proving that he his fully recovered from his knee injury.
Lars Hirschfeld made his first start for United, but he didn't make the impact he hoped for as he gifted Kilmarnock the opening goal in the seventh minute.
Gordon Greer had the game's first attempt when he blazed wildly over in after six minutes after controlled build-up work from Allan Johnston, Invincibile and Boyd.
Boyd gave him a lesson in controlled finishing when Hirschfeld miscued his clearance from Alan Archibald's back-pass straight to him in front of goal 25 yards out.
With the keeper stranded wide of goal, Boyd stroked the ball purposefully into the opposite corner for his second goal of the season.
Killie continued to flood forward in numbers and Boyd claimed his second goal in the 15th minute. Again the offside trap was burst, this time Johnston sending Dargo free. Johnston found space in the area, but Dargo crossed low across the face of goal for Boyd to bundle the ball past Hirshfeld's despairing dive.
Despite having centre-halves filling all four defensive berths, Killie allowed United to grab a goal back from a set-piece. Barry Robson's inswinging corner from the right was met by the unmarked Archibald who volleyed home from seven yards.
Killie restored their two-goal lead five minutes later as Boyd completed his first senior hat-trick.
Grant Brebner lost possession cheaply on halfway to eter Leven. The impressive midfielder drove at the defence before playing an inch-perfect pass into the striker's path and he drilled the ball low past Hirschfeld.
Boyd's day got even better two minutes later. Invincibile skinned Archibald forcing the defender to bring him down inside the box. Boyd stepped up and beat the keeper low at his left corner.
Boyd even had a goal chalked off as he was adjudged to have climbed on Archibald to head Dillon's corner kick home.
The second half was expectedly tame, but United sparked some life into proceedings with 12 minutes left. Stuart Duff's shot deflected into the path of Billy Dodds, who turned and fired past Alan Combe from a suspiciously offside position.
Killie would have the final word and Boyd scored his landmark goal in the final minute. Again Invicibile was the architect as he drove the ball low for Boyd to force home from close range.