A combination of Hearts advantage in physique and experience led to the Tannadice teenagers slumping to defeat in the opening league fixture of the season at North End Park yesterday afternoon.
Striker Dennis McLaughlin was hat-trick-hero for the visitors, and also set up the opener, playing in Jamie Mole to net from just inside the box after only four minutes.
That lead was doubled just three minutes later when McLaughlin was on the end of a deep cross to head home at the back post.
Clawing their way back into the game, United went close to pulling one back midway through the first period when David Goodwillie's follow up effort after Marco Andreoni hit the bar was scrambled to safety.
And six minutes later Andreoni bravely headed a David Gray free-kick from close range to give the tenacious Tangerines hope.
Enjoying their best spell of the game, a great finish from Martin Feeney after he had driven into the box restored parity nine minutes from the break.
However, slackness at the back allowed McLaughlin to crucially put Hearts back in front a couple of minutes from the break.
The game was effectively put beyond the United youngsters four minutes into the second half when McLaughlin completed his hat-trick with a shot on the turn from 15-yards.
With 25-minutes left, the scoring was completed the ball when an unchallenged John Armstrong drilled home a fifth from just inside the box.
United: Gibson, Flynn, Gray, Burnett, McMechan, Donnelly (Travers 74), O'Hara (Watson 78), Andreoni (Milligan 84), Feeney, Goodwillie, McCord.
Subs not used: Paterson, Russell.
Hearts: Barjaktarevic, Thomson, McDonald, D Armstrong, Lithgow, J Armstrong (Forker 72), Doherty (Bjornsson 85), Mole, McLaughlin (Slater 83), Neill, Diver.
Referee: Jim Lyons