United's play-off hopes are hanging by a thread following Saturday's defeat at Birmingham City.
Despite, Mark Duffy's goal, the Blades were unable to hold out and now face a tough ask to reach the top six with just two games to play.
Duffy and Donaldson were recalled to start against their former club. Brooks dropped to the bench after a hectic period of games and Clarke was not included after a back spasm in training. Moore (tonsillitis) and Wright (knee) missed out so Eastwood, Holmes and Wilson were added to United's bench.
Jota scuffed an early shot wide for the home side but United were the quicker into a rhythm - emphasised by the opening goal on seven minutes. Birmingham were caught on the break and after a searching ball from Evans, DUFFY twisted and turned before beating Stockdale at his near post. The subsequent celebration saw the scorer booked.
Another breakaway almost brought United a second but Stockdale this time tipped over a curling Evans shot. Fleck just failed to attach himself to a Baldock cross as United remained on top.
The home side hit back just before the half hour, Kieftenbeld's shot from 25-yards took two deflections and Morrison met a Maghoma free-kick but Blackman was well placed to collect. The equaliser, though, arrived on 32 minutes. From Maghoma's corner, Jutkiewicz took the attentions of defenders before ROBERTS sidefooted home at the near post.
United were pegged back for a spell but Birmingham's next chance was 25 seconds into the second period when Blackman pushed away a header from Jutkiewicz.
Boss Wilder threw on another striker, sacrificing a midfielder, confirming his intentions but on 69 minutes Birmingham edged in front. The pace of MAGHOMA got him clear and he slid the ball past Blackman.
Brooks replaced Duffy but the young Welsh international was injured soon after as he took on Morrison. After a period of treatment, in which to stretcher entered the pitch, Brooks was able to continue.
The final 20 minutes saw United on the front foot but unable to cause undue problems for the home defence. Wilson replaced Donaldson but again the chances were sparse.
Blackman had to deflect a shot from Harding wide on the break, whilst Sharp almost got a touch onto a Brooks chip over the defence. Soon after, Baldock was unable to turn his header towards goal from Sharp's cross.
Six minutes of injury-time offered hope and Blackman added his height to the Birmingham box for a late free-kick but an equaliser was not forthcoming.
Birmingham: Stockdale, Roberts, Colin, Kieftenbeld (Gardner 61), Jutkiewicz (Gallagher 86), Adams (Ndoye 90), Maghoma, Davis, Jota, Morrison, Harding.
Unused: Grounds, Boga, Dacres-Cogley, Kuszczak.
Blades: Blackman, Baldock, Stevens, Fleck, O'Connell, Basham, Lundstram (Sharp 59), Donaldson (Wilson 81) , Stearman, L Evans, Duffy (Brooks 70)
Unused: Leonard, Lafferty, Holmes, Eastwood.