United's Under 18s went down 1-0 at home to a solid Watford side after a Jack Burchell strike right on half-time was enough to down the Blades.
After a first half stoppage time corner fell his way, Burchell struck into the corner from close range, leaving Sam Kelly with no chance on an afternoon where chances were few and far between.
Chances were so rare that only Tom Weaver's looping header over the bar from a corner could be classed as a goal scoring opportunity for a young Blades side which held their own well against more experienced opposition.
Watford largely controlled the ball but did little with it, United putting in a dogged defensive performance to keep their visitors at bay until near the break.
Neal Harrison did whip a curling effort just wide shortly before half-time before Watford scored what would turn out to be the clincher.
United failed to clear a corner from the left, leaving Burchell the easy opportunity to fire the ball low into the corner from near point-blank range.
The second half provided much of the same for both sides as United put the pressure on but Watford held steady throughout the half.
Zak Brunt did trouble the Watford goalkeeper with a low effort from outside the box minutes after the restart but the Blades could only rely on half chances on what became a frustrating afternoon at Shirecliffe.
Some neat footwork from Ompreon threatened to undo the Watford defence at times but all too often their defence came to the rescue to thwart any sight United got of the goal.
A curling, whipped in cross just avoided the heads of several United players in the dying minutes while Watford appealed for a late penalty on the counter, but the referee was having none of it.
Blades: S. Kelly, Williams, Foulstone, Weaver, Neal, Belehouan, Stainrod (J. Kelly 61), Broadbent (Ackroyd 66), Potts, Brunt, Ompreon (Viggars 86).
Unused: Chapman, McGuire.