United confirmed a place in the end of season play-offs with another vital point.
With a game to spare, the Blades can now make plans for the May games following Saturday's encounter at Leyton Orient.
After dominating, Mathieu Baudry gave the home side the lead but Bob Harris levelled with a deflected effort.
United went close to winning it late on when Jose Baxter's free-kick struck a post.
Harris returned from injury and Adams was given a start in the capital clash. Kennedy missed out with his knee problem, whilst Doyle dropped to the bench as boss Clough made two changes and handed the captain's armband to Brayford. With Turner, Done and McNulty also injured, the bench included three homegrown teenagers.
In bright Brisbane Road sunshine, the game's first opportunity fell to the Blades and it should have been the lead. A one-two between Davies and Holt saw the latter in the clear but his shot was too close to the body of goalkeeper Cisak.
United were the better team in the opening 20 minutes, with plenty of possession in the Orient half. Murphy's near post shot was saved after good work involving Harris, Holt and Adams, who also had a shot at goal soon after.
The later stages of the period were more even with Orient registering a couple of efforts. Dagnall's shot was comfortable for Howard, who also helped a powerful drill from Batt over the crossbar.
Just before the break, the Blades went close again, following a break from an Orient corner. A run from Murphy saw an Adams shot blocked, the follow-up saw Cisak save from Murphy and before the danger was over, Coutts fired over the crossbar.
The first effort of the second half saw the Blades on the offensive but a powerful first time effort from Adams was parried by the surprised Cisak. For the home side, after good work by Simpson, Cox fired at Howard.
Coutts and Baxter picked up yellow cards, whilst midway through the half teenager Calvert-Lewin was introduced for his debut, going up front, with Scougall coming on as a substitute. However, within minutes, the Blades were behind. From a Cox corner, BAUDRY timed his run to powerfully head past Howard.
The goal prompted a spell of Blades pressure and chances. In a crowded box, Scougall attached himself to Murphy's cross but Clarke made a last-ditch block. Brayford's shot from range was deflected wide and from the resulting corner, the ball broke to Basham but his effort on the turn was over.
An equaliser was moments away, though, with United firmly on top. Freeman did the hard work, making tracks across the box before Baxter laid off for HARRIS to score with a long-range effort, helped by a deflection.
The final ten minutes saw both sides wanting to push for a winner. Following a foul on Holt, a 20-yard Baxter curling free-kick cannoned against a post, whilst at the other end Harris was booked and a Simpson free-kick was turned over by Howard.
Doyle was introduced as five additional minutes were announced and the closing moments were nervy at both ends with the game stretched but there was no further goalmouth incident as the final hurdle to secure a play-off place was safely cleared.
Orient: Cisak, Omozusi, Cuthbert, Baudry, Cox, James (Wright 62), Batt (McAnuff 52), Clarke, Bartley (Mooney 86), Dagnall, Simpson.
Unused: Lowry, Woods, Hedges, Taylor.
Blades: Howard, Harris, Brayford, Basham, Murphy, Baxter, Coutts (Doyle 90), Freeman, Adams (Calvert-Lewin 66), S. Davies (Scougall 66), Holt.
Unused: Alcock, Willis, B. Davies, Reed.