IT was the decision that defined a dynasty. And Archie Knox recalled last night how he tried to talk Sir Alex Ferguson out of it.

Who knows what might have transpired if the Manchester United assistant manager's argument had won the day, and Jim Leighton had kept his place for the FA Cup final replay with Crystal Palace some 26 years ago? All posterity shows is that he was overruled, leaving the previously untouchable Scotland goalkeeper facing the national embarrassment of being dropped after a hesitant performance in a first match which had ended 3-3 after extra time. His jersey went to the eccentric figure of Les Sealey - who promptly became a folk hero as a solitary Lee Martin goal landed Ferguson's first major title at Manchester United.

"I would have gone with Jim again, there's no doubt about it," said Knox, who had followed Ferguson from Aberdeen when he arrived at Old Trafford in November 1986. "I thought the goals could have been prevented by the defenders so I came out on Jim's side on that occasion. But Alex said 'no, we need to make the change'. So fair enough. You go ahead with that and it was proved right at the end of the day.

"That is just what happens in football," he added. "Managers have to come up with these big decisions and throughout his career Alex Ferguson hasn't got many of them wrong. You can't argue with that. Although you can put up your own case at the time, as I did. I don't think you would have lasted with Alex if you didn't have an opinion."

While this pattern of humiliating high-profile stars would be a coda throughout Ferguson's remarkable managerial career at Old Trafford - it spanned 27 years and harvested a further 37 major honours - few decisions were as bittersweet as this one.

As you might expect, Leighton - who would be trusted by Ferguson to start just one more match, a League Cup tie against Halifax Town, then placed 92nd in the English league - took his sudden fall from grace hard. On hearing the news, Sealey sought him out to console him, only to find the Scot in tears. He even presented him with his winner's medal afterwards, only for Leighton to quietly slip it back into the pocket of the Englishman's blazer.

“I said to him ‘see if it was round the other way, you wouldn’t accept it, would you?’," recalled Leighton a few years ago. "He said ‘no’. I said: ‘well, I am not interested’.”

Leighton, who would go on to play some of the best football of his career with Hibs and Scotland in the late 1990s, actually earned a winners' medal by dint of his performance in the first match, but quietly sent it back to the Football Association via Royal Mail. The indelible bond between the two goalkeepers was such that Leighton helped carry Sealey's coffin after his untimely death to cancer at the age of just 43.

"Listen, these guys understand that these things can happen," says Knox. "Okay they are bitterly disappointed, and it is a major setback to them. But you have got to get on with it. The only thing you are guaranteed in football is your disappointments. If you lose your place, get an injury or whatever, then you are gutted but you can't allow it to fester. If you are going to be one of the top ones you have to get over it and get ready for the next bit."

While it would be wrong to overstate the case, the predicament Louis van Gaal finds himself in today's showpiece against the same opposition in the same, albeit remodelled stadium, could be said to be a modern variant of those early faltering days of the Sir Alex Ferguson era.

It seems ridiculous with hindsight to say it, but patience in some quarters was running out. While an 11th place finish in the first season was creditable considering the team he took over was languishing in the relegation places, and United finished second to Liverpool in Ferguson's first full season, that progress seemed to be stalling. A promising title challenge in the 1988-89 season petered away to another mid-table finish and here they were, back in the relegation places, come December 1989.

Four away ties in the FA Cup, famously against Nottingham Forest, then Hereford United, seemed only to offer further misery, even if the legend that Ferguson had been instructed he would not survive third round defeat at the City Ground is in fact an urban myth.

"That wasn't true at all," recalls Knox. "I can remember coming off the bus at the City Ground and Alex saying to me that Martin Edwards [the chairman] had said to him that 'no matter what happens today you will still be our manager'. I think people recognised what was going on and the steps that were being taken to get Manchester United back to the top again.

"But I can remember being 0-0 against Hereford in Hereford [the fourth round] with a minute to go and the Hereford boy was right through on Jim Leighton," he added. "Someone in the crowd blew a whistle and the Hereford boy stopped. Then someone, Mick Duxbury I think it was, got back and stopped him. We went right back up the park and scored through Mick Duxbury."

The rest, as they say, is history, even if that first 1990 final was a fraught business. Goals from Bryan Robson and Mark Hughes had cancelled out Gary O'Reilly's early opener, only for two goals from substitute Ian Wright to leave Steve Coppell's excellent Palace side minutes away from victory. That was until Hughes lashed in his second of the day in extra time. It was a different matter in the replay, though, the silverware enough to gloss over a 13th place league finish that year. From then on, it was sixth (plus a Cup Winners Cup success) and second (plus a League Cup success) before the first of 13 top division titles arrived in the summer of 1993, two years after Knox had left to join Walter Smith at Rangers.

"I think we had already established in our minds that we were going to be successful, we just needed to get over that first hurdle," said Knox. "Winning the FA Cup, albeit after a replay, that was the big turnaround if you like. We had put everything we had put in place with the local scouting and stuff like that, to stop Man City getting all the local kids. But it started the whole thing off.

"The only thing I regret from the day was not getting a video or photograph of me dancing on the platform with Sir Matt Busby afterwards," he added. "That was getting the train back up to Manchester, I'm not sure whether it was from King's Cross or Euston."

Not even the Louis van Gaal himself would predict a Ferguson-style 25-year trophy haul for himself at Old Trafford, but the Dutchman has a year left on his current deal and might just be allowed to see it out if, as Knox suspects, he watches United collect the first major trophy of the post-Ferguson era. He, though, will be at Hampden Park to watch the Scottish Cup final.

"I don't have any info about it but I think he [Van Gaal] would see out his contract," said Knox. "He has another year left, I don't think he has any ambitions any further than that. But it would be great way for him to kick off his bit of it by winning the FA Cup, which I think they will anyway.

"[The club struggling in the post-Ferguson era] was always going to be the case," he added. "I don't know why people are surprised by it. To follow that was always going to be difficult, no matter who it was, [Jose] Mourinho, Van Gaal, [Pep] Guardiola the whole lot. Whoever you want to mention, none of them compare to Alex's achievements."