United rounded off 2016 with a victory, thanks to Kieron Freeman's late goal.
In front of the Kop the defender pounced to frustrate Rob Page's hard-working Northampton Town team.
Manager Wilder made a tactical change in attack with Clarke taking over from Done, who dropped to the bench and was joined by Reed.
For the early kick-off there was a bright start and both sides had two half-chances each in the opening five minutes. Fleck's shot was blocked and Sharp was off target from a quick throw inside the first 60 seconds and then, for the visitors, Anderson snatched at a half-volley and Fleck blocked an effort from Hoskins after a quick break.
United's first corner saw Sharp head over at the back post from Fleck's delivery and the skipper laid off for Coutts to side-foot wide on 12 minutes.
Again Northampton hit back with a chance, Anderson headed wide a Phillips cross, but the Blades were attempting to exert authority and Duffy had a free-kick deflected wide before curling into the goalkeeper's hands. Northampton, though, were well organised in protecting their goal and were a threat on the break, emphasised by Ebanks-Landell having to pick up a booking for a foul on Hoskins.
The best chance of the period fell to United on 36 minutes as the pressure mounted but from Freeman's low delivery, Clarke could not connect from inside the six-yard box. In addition, Clarke's header from O'Connell's cross in injury-time was wide.
In a slow start to the second half all United could muster was a Clarke header, which was wide, resulting in Wilder making a change - Lavery was introduced before the hour mark.
United were seeing lots of the ball without creating many chances, resulting in Scougall also being introduced and a change of system. Duffy had an effort blocked and just before departing, Basham held up a cross for Sharp, whose effort struck the outside of the back post.
Fleck was off target as the final ten minutes approached and Wilder's final change was a bold one, replacing Lafferty with Done
Northampton's best chance (their only one of the second half) was a 35-yard free-kick from Taylor on 82 minutes and Moore produced a tremendous save at the top corner.
Duffy shot wide and Lavery had an effort blocked before the pressure finally paid off. Coutts progressed down the right, shouted to Ebanks-Landell to get out of the way, and delivered a low cross which Nyatanga blocked but FREEMAN was ideally placed to blast into the roof of the net - delighting the Kop.
There was one more chance in injury-time, also for United. Lavery broke through and after Smith's initial save, Scougall volleyed against the top of the crossbar. It wasn't to prove costly as United moved onto the 50-point mark.
Blades: Moore, Fleck, O'Connell, Basham (Scougall 69), Sharp, Coutts, Freeman, Ebanks-Landell, Duffy, Lafferty (Done 81), Clarke (Lavery 58).
Unused: Ramsdale, Wright, Brown, Reed.
Northampton: Smith, Buchanan, Anderson (Potter 69), Zakuani, Richards (Beautyman 86), Revell, Hoskins (Iaciofano 90), Phillips, O'Toole, Nyatanga, Taylor.
Unused: Diamond, Gorre, McCourt, Cornell.