United remain top of EFL League One following another home victory on Saturday.
Despite conceding early to a Ricky Holmes free-kick, goals from Jack O'Connell and Daniel Lafferty were enough to see off Karl Robinson's side and make it nine games unbeaten for Chris Wilder's leaders.
For the fixture against the Addicks, boss Wilder made two changes from the starting XI at Swindon, with Duffy and Hanson return in place of O'Shea and Lavery, who are named amongst the substitutes.
Charlton were quickly out of the blocks and took the lead in the third minute. United failed to clear the ball on two or three occasions, before Coutts fouled Forster-Caskey and from the resulting free-kick, HOLMES dinked an effort over the wall and into the corner of the net, beating the dive of Moore.
The visitors continued to force the issue and after Bauer had nodded down a left-wing corner from Holmes, the crossbar saved the Blades following Watt's acrobatic effort. Moore the saved comfortably from Konsa.
But with the first attack of note, the Blades restored parity in the 14th minute. The visitors failed to clear their lines from a free-kick and in the second phase, Duffy sent in a pinpoint cross that was glanced home by O'CONNELL. In response to conceding, Charlton got back on the front with Holmes firing over from a promising position, after Lafferty had done the same for United.
Just before the half hour, referee Duncan was unpopular amongst the home faithful as he waved away appeals for a penalty, after Fleck was grounded looking to get on the end of a Hanson knockdown. At the other end, Moore was alert to divert a Watt round the post at the expense of a corner.
With half-time approaching, the Blades came so close to taking the lead. Some neat build-up play saw Lafferty thread the ball through to Sharp and having beaten the offside trap the skipper's ball across the face of goal agonisingly missed the outstretched boots of both Fleck and Hanson at the back post. Then, from another Sharp cross Bauer almost miscued the ball into his own net. The chances continued to come, this time Ebanks-Landell heading over from Coutts's deep corner.
Within two minutes of the restart, the Blades had a sight of goal, but Sharp header wide from Fleck's corner. But 60 seconds later, United hit the front. Coutts and Freeman combined on the right and the latter picked out LAFFERTY at the back post, his header was saved by Rudd, but the Northern Irishman reacted first to tap home in front of the Kop.
The visitors could have equalised soon after, but Holmes fired almost into the top tier of the Bramall Lane end, after Forster-Caskey and Watt had crafted an opening. Minutes later, Konsa missed an even better chance from close range from Forster-Caskey's right-wing cross.
Shortly after the hour, Duffy received warm applause as he was replaced by Carruthers. United continued to be positive and after Holmes had fired over again at one end, Basham headed just off target from Fleck's free-kick, before Carruthers hit a first-time effort into the side netting. For the second time in the game, the referee waved away appeals for a penalty as Rudd and Sharp tangled.
With six minutes remaining O'Shea replaced Coutts and the substitute almost had an immediate impact, firing just over with a first-time strike after a run by Lavery. With the clocking ticking the home fans made the Lane a cauldron of noise. Three minutes of added time were signalled by the fourth official and backed continuously throughout, the Blades saw the game out without any alarms.
Blades: Moore, Fleck, O'Connell, Basham, Sharp, Coutts (O'Shea 84), Hanson (Lavery 73), Freeman, Ebanks-Landell, Duffy (Carruthers 63), Lafferty.
Unused: Long, Lavery, Done, Wright, Chapman.
Charlton: Rudd, Chicksen (Dasilva 84) Bauer, Watt, Holmes, Konsa, Ulvestad (Botaka 80), Forster-Caskey (Crofts 73), Byrne, Novak, Teixeira.
Unused: Jackson, Phillips, Ahearne-Grant, Hanlan.