A solitary goal midway through the first half earned the visitors three points from a disappointing encounter at Station Park, Forfar.
After a bright start, it was something of a flat performance by the Tannadice side, albeit there were seven members of the youth side in their ranks.
United created the first opening after five minutes. A goal seemed certain when Scott Paterson headed a Fraser Mulligan cross back across goal, but Jonny Russell and Greg Cameron got in each other's way and Russell's header failed to hit the target.
The feet of Euan McLean came to United's rescue on 16 minutes when he blocked a Mark Stewart low shot with his feet.
But hesitance at the back seven minutes later enabled Falkirk to score what turned out to the only goal of the game.
Ronan Wallace chased a long high ball out of defence, shrugged off the challenge of Garry Kenneth before lobbing the ball over the advancing McLean.
United almost equalised just after the half hour mark when the ball broke to David Goodwillie in the six-yard box, but the legs of keeper Robert Olejnik kept out his effort.
Thereafter, Falkirk created the clearest scoring chances. A Carl Finnigan drifted narrowly past the post before the break and only a brilliant one-hand save by McLean denied Kevin Moffatt's raging drive ten minutes into the second half.
And just before the end, Finnigan was through on McLean who saved his first effort and the striker knocked the rebound wide of the empty net.
Dundee United: McLean. Mulligan, Fleming (McGrath 62), Cameron, Kenneth, Pope, Kerr, Ryan McCord, Goodwillie, Paterson, J Russell. Subs not used: Gibson, McGrath, Mathieson, Ross McCord, Love, Anderson.
Falkirk: Olejnik, Gibb, Craig, Allison, Scobbie, Moffatt, Arfield, Mitchell, Wallace, Finnigan, Stewart (Sludden 73). Subs not used: Andres, Staunton, McMahon, Jeffrey.