The Blades began brightly at the Madejski Stadium, Leon Clarke spurning two chances in the opening stages of the match, before the deadlock was broken on 11 minutes.
The Royals struggled to cope with United's attacks and they duly conceded a second goal on the stroke of half time.
Mark Duffy cut in from the left and, from the edge of the area, rifled a ferocious effort towards goal which beat Mannone at his near post.
Jaap Stam's men were booed as the half-time whistle blew but they claimed a lifeline when, on 52 minutes, Omar Richards converted from a tight angle after Leandro Bacuna's free kick was parried by substitute goalkeeper Simon Moore.
Reading then had a chance to draw level when Liam Kelly was brought down on the edge of the Sheffield United box for a penalty, but Bacuna's spot kick was parried behind by Moore.
Just moments after almost claiming an equaliser, the hosts fell two goals behind again as Sharp ran on to a diagonal ball from John Fleck and volleyed home his second of the game.
The Blades had to be alert in the final stages of the encounter as Chris Martin drilled a low effort wide from a dangerous position, but the final whistle eventually blew on a three-point haul for the Yorkshire side.
Victory for United puts them sixth in the Championship table, while Reading remain 18th in the standings.
READING (4-4-2): Mannone; Bacuna (Evans 67'), Gunter, Moore, Ilori (Smith 74'); Van den Berg, Clement, Kelly, McCleary (Richards 6'); Bodvarsson, Martin
SHEFFIELD UNITED (3-4-1-2): Blackman (Moore 34'); Basham, Stearman, O'Connell; Baldock, Evans, Fleck, Stevens; Duffy (Leonard 82'); Clarke (Donaldson 34'), Sharp