Two goals from Reon Potts, saw United's U18s rally from going behind to register a first victory of the season at Shirecliffe on Saturday.
But the Blades, who entered the game on the back of consecutive losses, fell behind inside three minutes, as a squared pass led to the Hornets opening the scoring.
United recovered though and restored parity in the 20th minute. After Lawrence had headed over, Greaves was again the provider from the left and POTTS arrived at the back post to stab home from close-range.
The lively Greaves was involved again as United looked to continue the forward momentum, but after a driving run from the winger, Doherty saw his acrobatic effort cleared by a retreating defender.
But on the stroke of half-time the turnaround was complete. Greaves whipped in a corner from the left and after Lawrence headed against the crossbar, it was POTTS who reacted quickest to tap home the rebound from a yard out.
In what turned out to be a much more subdued second period, it was Watford who again pressed forward during the opening exchanges, hitting the post with a header.
And goalkeeper Warhurst was again relieved to see the woodwork come to his and the Blades rescue as the clock began to tick down, before Belehouan made a crucial last-ditch block to stop the rebound being converted.
The last action of note, saw substitute Mason race clear on the break and he looked destined to make three, only to fire narrowly wide of the far post.
Blades: Warhurst, Hawkes, Foulstone, Cutts, Gordan, Belehouan, Broadbent, Doherty, Lawrence (McClellen 74), Greaves (Ompreon 88), Potts (Mason 64).