Stevie Campbell's youngsters eased their way to victory in the 'wee derby' at Dens, repeating the four goal winning margin of the first 'wee derby'.
Just six minutes had gone when Robert Thomson collected a pass from Ross Gilmour and from an acute angle wheeled to fire a left-foot volley just inside the far post.
Dundee came close to levelling four minutes later when Joe McGovern failed to hold a Connor Macleod shot. Gary Duggan was first to react as the ball ran loose to send it back across the face of the goal but fortunately there were no takers.
Thomson almost doubled United's lead but his netbound header was cleared off the line.
However, on 17 minutes, the lead was doubled, this time Thomson supplying Scott Smith who fired home through the keeper's legs.
United added after 27 minutes and Thomson was again involved, feeding Jordan Moore out on the right. Moore brushed away a challenge before powering his way into the box to hammer the ball high into the net from 15 yards.
The second half was only three minutes old when to John Souttar's long ball found Ryan Ferguson who, having beaten the offside trap, expertly pulled the ball down before slipping the ball past the advancing keeper.
Only an excellent double save from McGovern denied Dundee a consolation counter, first blocking a Kevin Buchan effort and then keeping out a Gary Duggan shot.
Content to run down the clock, United almost added a fifth in the dying minutes when substitute Ryan Gauld, back after illness, went on a mazy run only to be thwarted by home keeper Alex Baird.
United: McGovern, Lundie (Gauld 58), Souttar, Johnston, Gilmour (Allan 77), S Smith, Petrie, Thomson, Fraser (M Russell 77),Ferguson, Moore. Subs not used: Anderson, Bell, Spark, B Smith.