United's hopes of making the Professional Development League end of season play-offs are over following defeat at the Macron Stadium.
David Brooks put United, who named four trialists in the starting XI, in front early on with a free-kick, but the concession of three second-half goals and the dismissal of striker Jake Wright condemned the Blades to defeat, despite goalkeeper Jake Eastwood saving a penalty with the scores level.
It was a bright start with both sides threatening early on. The lively King fired wide for the home side following some neat work down the right-hand side, however, it was the Blades that struck first in the ninth minute.
BROOKS dusted himself having been fouled and curled home a free-kick, beating goalkeeper Jaaskelainen at his near post.
Chances were at a premium as the half wore on, but United had an opportunity to double the lead with Brooks again the catalyst. First, he fired wide after carving out his own opportunity with a fine run, and then side-footing just over the top following good work from Wright.
In response, King again struck just wide of the post for the home side as United saw the half out on top with trialist Hinkson drawing a stop from Jaaskelainen on the angle.
As the second-half got underway, United were quickly out of the blocks with Wright being denied. But it was the hosts who were soon level as PERRY worked a shooting opportunity from 20 yards before firing low beyond Eastwood.
The game then turned decisively in the hosts favour when the referee spotted an infringement in the area from a corner and awarded a spot-kick. Wright was dismissed in the aftermath before Newell saw his penalty palmed clear by Eastwood diving to his left.
With the hosts now firmly on top, Perry found the overlapping Spooner on the right, but his driven effort cannoned off the crossbar, before Eastwood was called into action once again with an acrobatic stop to deny King.
But there here was nothing Eastwood could do on 76 minutes however, as EARING rose at the far post to head home from close range following a short corner, before substitute SAMIZADEH put the game to bed with a perfectly weighted lob over the onrushing Eastwood with three minutes remaining.
Blades: Eastwood, Bennett (Ferguson 36), Kelly, Reed, Lees, Taylor, Hinkson (Parkhouse 56), Doherty, Wright, Brooks, Worrall (Portman 82).
Unused: Perryman, Brown.