The U19s were held by their Perth counterparts at a windy and wet St Andrews yesterday afernoon.
Backed by the elements in the first half, United had a clutch of chances.
Scott Allan and Dale Hilson went close before Ryan Dow had a shot cleared off the the line after 32 minutes.
But United did break the deadlock two minutes from the break when Dale Hilson headed home a cross from Grant Mosson after a surging run by the full back.
In the second half the wind picked up and adopting a direct approach, it was Saints turn to dominate.
Striker Stevie May forced a couple of good saves from Mark McCallum, but on the break United still threatened
However, six minutes from the end, Liam Caddis squeezed home the equlaiser after the United rearguard failed to clear their lines.
Even then, United have snatched victory as they finished strongly, with Hilson firing into the side-netting after rounding the keeper would have proved more profitable with team-mates in the box.
Just after the final whistle United's Ryan Dow was red-carded for remarks to the referee, picking up a second yellow to add to the ludicrous booking he received for diving in the first-half when he had clearly been fouled.
Dundee United: McCallum, Irvine, Hill, Shaw, Mosson, Allan (Elfverson 70), Stokes, Lee, Armstrong, Dow, Hilson. Subs not used: Robertson, McCulley, Murray, L Swanson.
St Johnstone: Duffy, Porter, Alexander, McIntosh, Durnan, Lindsay, O'Hare, Steeves (Walton 70), Heagney, May, Caddis. Subs not used: Clark, Breen.