'Bestie promised me a bottle of champagne!'

Coincidentally, the anniversary falls on the very same day that the Reds and Blues are set to meet again, with this weekend’s Premier League fixture at Old Trafford set to kick off at 12:30 GMT.

McIlroy was astonished to learn that fact when he sat down with us to reminisce about his maiden game for the club, and admits he still remembers his first match like it was yesterday.

“It’s unbelievable,” said the club legend. “When I first found out at the beginning of the week, [that it’s] 50 years to the day, I just thought: time has flown by! But it is unbelievable: it is actually 50 years since my first debut for Manchester United against Manchester City.

“[I remember] everything, everything, believe it or not. From Friday, going into training… Bill Foulkes , who was Reserves-team trainer at that time, saying: ‘You won’t be playing tonight in the mini-derby against City Reserves. Report tomorrow, 11 o’clock, Old Trafford, for the first team. Make sure you wear a collar and tie. Get on with training.’

“That’s all he said to me!”

McIlroy had only turned 17 three months earlier, so the nerves must have been jangling at this point. But despite the prospect of playing alongside Ballon d’Or winners Bobby Charlton and George Best – and in a United side that had won the European Cup only three years earlier – the Northern Irishman took it all in his stride.

“I went into where I was supposed to go to, to see the rest of the squad, and I was told to go up to see [manager] Frank O’Farrell who was in his office,” remembers Sammy, who would go on to play an impressive 419 matches for the club.

“I went to see Frank, and Frank told me that Denis [Law] had failed a test and I would be playing. That’s all he said to me.

“Bestie was one of the first I met when I came down the stairs. He said to me: ‘Right, score a goal today and I’ll buy you a bottle of champagne.’”

And it didn’t take the teenager long to make a lasting impression at Maine Road. In the 39th minute, he combined with his compatriot Best to give United the lead.

“I remember the build-up,” he recalls. “George had a run with it, played it out to Brian Kidd on the right-hand side. I just kept running into the box; Bestie did that as well.

“The ball from Kiddo came in towards George, George tried to stop the ball and control it, but [City defender] Tony Book was actually tugging away at his shirt and there’s me following up. The ball ran loose and I just side-footed it past Joe Corrigan. An unbelievable feeling.

“But I actually think, when I look back at the goal, if I wasn’t in that position, I’m sure we would have had a penalty, because Tony Book was tearing the shirt off Best. But, because I was there, the referee probably played advantage and I just slid it past Corrigan.

“It was unbelievable. There was 63,000 people there was well. The atmosphere was absolutely electric, and I’d never experienced an atmosphere like it that before, in my time. It was just unbelievable. For all the players to come towards me – Bestie, Bobby, Brian Kidd, Willie Morgan – to be the first around me, it was unbelievable.”

McIlroy went on to play in three FA Cup finals for the club – including the famous 1977 triumph over Liverpool – but says memories of his debut still send a shiver down his spine.

“It was end to end. It was one of the greatest games I’ve played in. You played for the supporters – you didn’t want to let them down – and it finished 3-3. But [it was] a fantastic game to play in and, for my debut, I’ll never forget it.”

Watch the video above to see McIlroy’s memorable first United goal, and hear recollections from Sammy himself plus team-mate Alex Stepney.