At Stocksbridge on Monday afternoon, the Blades deservedly ended Hull City's start to the U21s season.
Goals from Connor Dimaio, Jake Wright and CJ Hamilton capped a fine performance from Chris Morgan's young grafters.
United bossed the first half and coach Morgan would have wondered how his team were not ahead. On four minutes, Wright almost attached himself to a short back-pass and McDonagh headed home but he was adjudged to have pushed a defender before connecting with a deep Phillips cross.
McDonagh also fired into goalkeeper Watson's arms before the Blades took the lead with a neat move on 28 minutes. After finding Hamilton with a pass, DIMAIO continued his run into the box and slotted home a controlled sidefooter from six yards.
Further Blades chances followed. Wright shot just wide after good work from Heh and then the same striker skimmed the crossbar with a free-kick before Hull levelled with their first and only chance of the half; there were numerous chances to clear before ANNAN beat Long from an acute angle.
Early in the second half there were chances for both sides to edge in front. Quick Dimaio feet set up McDonagh, who was denied by the goalkeeper, then Olley chipped over the crossbar for the visitors.
The endeavours of McDonagh, who hunted down three defenders, set up Wright to scuff wide on 58 minutes and then Annan curled in a free-kick into the arms of Long.
On 71 minutes, United had a great chance to grasp the initiative from the penalty spot. McDonagh got on the end of Long's kick and drew a foul from Aimson but from the resulting spot-kick, goalkeeper Watson saved Whiteman's effort.
Long was called upon to stop Bowen soon after but the Blades were on top and Watson again saved when Khan and Hamilton combined on the right. However, he could do little about the home side regaining the lead on 77 minutes. A melee from a corner saw both sides appealing for decisions before WRIGHT escaped three defenders in close proximity ahead of slotting home.
Late on McDonagh shot across goal and wide, whilst Hull's best chance of a second leveller fell to Dixon, but his shot skimmed the outside of Long's right post.
Injury-time saw Long make an impressive save to keep out Bowen, who was in the clear, before United clinched the victory with a goal on the break. McDonagh held the ball up before finding HAMILTON in space and he slammed home past an exposed Watson.
Blades: Long, Khan, Phillips, Dimaio, Banton, Whiteman, Heh (Coustrain 69), Brooks (Adebowale 90), McDonagh, Wright (Slew 88), Hamilton.
Unused: Perryman, Burton.