Olly Groome reports from Bramall Lane
Sometimes, things are just not meant to be.
On an afternoon which promised so much at Bramall Lane, Charlton were sent out of the FA Cup by two quick-fire goals which saw their League One opponents through to the Wembley semi-final.
The 5,331 travelling Addicks certainly did not deserve what unfolded in South Yorkshire. The visitors failed to offer anything in the final third and, in truth, never looked like troubling Nigel Clough's defence, leaving the fans to head back down the M1 bitterly disappointed.
Chris Powell made a solitary change to the side beaten at Leicester City the previous weekend with Steel City veteran Marcus Tudgay making his first start for the Addicks alongside Simon Church up top with Astrit Ajdarević reverting to the bench.
And in a game played in an electric cup atmosphere Charlton looked to get forward early, yet cautiously.
Jordan Cousins' diagonally flighted ball saw Church racing to get on the end of it in the early exchanges but Blades' stopper Mark Howard, after an initial fumble, claimed the cross.
In the 11th minute, the hosts went on their first foray forward.
When Harry Maguire was allowed to saunter into Charlton's defensive half unchallenged, he was able to to supply a ball out wide.
But a United forward struggled to keep the ball in play and with a box packed full of Blades, the Addicks were relieved to see the linesman flagging for a goal-kick.
Back at the other end, and Church was presented with a half-chance after a good interchange with Tudgay.
Receiving a one-two back from his strike partner he let fly from 25 yards with a left-footed effort which was just too tame with Howard collecting safely.
And a minute later Callum Harriott tried his luck from similar range.
This time from the left, the winger cut in before striking straight at the hosts' custodian.
The first-half was carried out on a knife-edge but, in truth, little else was expected as the half-chances kept coming for both sides.
The home side showed a neat passage of passing play with 25 minutes on the clock before Jamie Murphy fired wide of Ben Hamer's right-hand upright from just outside the box as the pendulum swayed one way, then the other.
And the Addicks were next to chance their hand in attack.
Harriott did well to tee up Tudgay who's shot trickled goalwards leaving Howard scrambling. Although the goalkeeper got there, Johnnie Jackson worked hard to keep the ball in play before a cross back into the mixer was claimed well by the stopper.
Five minutes before the break United earned a free-kick when Jackson was booked for a foul on Ryan Flynn. And from the resultant free-kick, the Blades had the ball in the net.
With the ball half cleared by the Addicks it eventually made it's way back to Connor Coady who fired into the roof of the net one-on-one. But Charlton were saved by the flag and there could be no question that the striker was in an offside position.
As the half grew old, Charlton were struggling to maintain possession as the hosts grew in confidence.
Bob Harris rounded off the half when his shot from range curled just over the bar and, it was fair to say, the half-time whistle was a welcome sound for Powell's men.
The sides continued to feel each other out into the the second period with United the first to come close on 52 minutes.
Charlton dealt with a corner swung in from the right before the ball was pumped back into the danger area.
Maguire was on hand to receive possession with his back to goal 12 yards out, turning to fire a powerful shot into the side netting.
Then, with 59 minutes gone, the turning point came as Charlton missed a glorious chance.
A quickly-taken free-kick saw Tudgay win a footrace with Howard before looping the ball back into the six-yard box.
With the blades half clearing, it fell to Harriott 12 yards out but with no goalkeeper to beat, he fired his shot narrowly wide. It was a guilt-edged chance in a game where clear chances came at a premium.
Charlton would have to pray that they would not have to pay for that miss. Regrettably, on 65 minutes they did exactly that.
The Addicks failed to deal with Jose Baxter's diagonal ball leaving Ryan Flynn to nip in at the back post to control the bounce and loop over Hamer to make it 1-0.
And less than two minutes later, things turned disastrous when John Brayford's speculative shot took a wicked deflection off Richard Wood before spinning into the back of the net to leave Charlton 2-0 down.
The Blades' tails were up as they kept coming at Powell's side with Wembley feeling a million miles away.
The visitors could hardly get a kick and Bramall Lane erupted again on 77 minutes when they struck the post before the follow-up was knocked in. But once again, a flag saved Charlton from further despair.
Substitute Reza Ghoochannejhad did force a fine, point-blank save from Howard deep into injury-time but it was too little too late with referee Lee Mason blowing up moments later.
Charlton, quite simply, had no answer for their opponents as Sheffield United eased to their ninth straight victory to dump the Addicks out of the cup.
It must not be forgotten, however, that this season's unprecedented cup run has been nothing more than a welcome bonus. And although these runs are historically hard to come by in SE7, make no mistake, the Addicks will come close again. One day.
Charlton: Hamer; Wilson (Ghoochannejhad 71), Wiggins, Morrison, Wood; Cousins, Poyet (Green 71), Jackson, Harriott; Tudgay, Church (Ajdarević 65).
Subs (not used): Thuram-Ulien, Hughes, Dervite, Nego.
Booked: Jackson 39 (foul on Flynn), Harriott 71 (foul on Scougall)
Sheffield United: Howard; Harris, Brayford, Maguire, Flynn (McGinn 90); Doyle, Baxter (Davies 81); Collins, Coady, Scougall (Porter 86), Murphy.
Subs (not used): Hill, Miller, Long, Freeman.
Booked: Flynn 14 (foul on Harriott), Baxter 80 (foul on Green)
Goals: Flynn 65, Brayford 67
Referee: Lee Mason
Att: 30,040 (5,331 from Charlton)