Arsenal prevailed 2-1 in the first encounter, on 13 February, but in a manner that led the club to offer immediately to restage the game. United had kicked the ball out of bounds so their player, Lee Morris, could receive treatment for an injury. But Arsenal's Marc Overmars scored from a pass by Nwankwo Kanu following a throw-in that their team-mate, Ray Parlour, had directed towards the Blades' goalkeeper, Alan Kelly.
The FA was quick to sanctioned Arsenal's offer, and Fifa's president Sepp Blatter was full of praise for the gesture. On reflection, however, Fifa decided it had to discuss the issue, especially as no actual infringement of the laws had taken place, merely a contravention of the spirit of the law.
Arsenal's Tony Adams said he would have felt terrible if Fifa had banned the replay. The England defender was rested for the original tie, but said: "There's no way I could have lifted the trophy in May having not replayed this game. We want it to be played. We think it's fair that we start again even-stevens in the fifth round of the FA Cup."
Arsenal have sold 38,000 tickets at half price for the rematch, and Adams is delighted to play it again.
"It is the sensible and honest thing to do," he said. "A mistake has been made and the lads involved have thrown their hands up. I'm honest and I know the manager is honest and there's no way we could have gone through to the next round without having offered a replay.
"Personally, I was astonished that the game finished. I thought it would have been stopped before the end. I couldn't believe it when somebody told me we had played the last 15 minutes.
"A lot of possible scenarios have come to light since, but the referee played it the way he saw it. I think Steve Bould, who was the captain, suggested a few things but the ref said there was nothing he could do because no laws had been broken."
Arsenal's manager, Arsene Wenger, said it had not been easy to focus on the game.
"It has made things difficult," he said. "Yesterday, for the whole day, the game was on and off and the phone kept going. It was less difficult for the players because they didn't know. They just came in and said `do we play or not?' Twenty-four-hours before a game this is not the best way."
Arsenal, still glowing from their 5-0 demolition of Leicester City on Saturday, are without Martin Keown, Emmanuel Petit, Matthew Upson and Luis Boa Morte.
Wenger's Sheffield United counterpart Steve Bruce, who was incensed straight after the game and only placated by Arsenal's offer, also believed Fifa was wrong to leave it so late.
Bruce had asked: "It's quite farcical because, if they had something to say, why didn't they say it a week ago? Thousands of our fans have bought tickets and paid to go down there, so it appears strange for it to happen a week later. It seems a bit late in the day to change the decision."
Bruce looks set to keep faith with the same side which started the original game and drew with promotion-chasing Bradford City on Friday.
"We've prepared normally because, as far as we've been concerned, the game has always been on," he said. "The players have been focusing on a big game again and they want to play again. It's been a pretty hectic couple of weeks but from the outset, I've said I hoped common sense would prevail.
"Most of us in football aren't really interested in politics. All our lads want to do is get on with the game and play football again. The sad thing about the whole episode is we were only 12 or 13 minutes away from a proper replay back at our ground.
"It's difficult enough to go to Highbury once but it's even more difficult twice. We know it's a difficult task but we'll give it our best shot again. I thought our tactics were spot-on last time we were down there.
"We know we have to be at our maximum and catch them on an off-day but I thought we played extremely well in the first game, especially in the second half. I thought we caused them a few problems and got a foothold in the game."
Bruce has added the reserve goalkeeper Simon Tracey, Michael Twiss and Nicky Marker to the 14 on duty against Bradford, while around 4,000 United fans have bought tickets at pounds 8 each - half the price charged for the original tie.
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