The irony was not lost on anyone present when the fans packed behind the goal at the home end of AFC Wimbledon's tidy Kingsmeadow Fans Stadium in Kingston, West London broke into a song that, less than five years ago, they could never have imagined singing when a team in red from Manchester visited.
'We've got more fans than you, we've got more fans than you' they sang to the tune of La Donna E Mobile from Verdi's Rigoletto. It is a chant they know well after years of following the original Wimbledon football club, the club that was ripped from their collective hearts - and local postcode - when the FA criminally allowed Charles Koppel, a South African backed by Norwegians, to up sticks and move the club to Milton Keynes.
In years gone by, of course, they were more accustomed to hearing it than taunting their opposite numbers with it. When Manchester United won their first league title in quarter of a century back in 1993, the final game of that season was against Wimbledon. 30,115 were in attendance at Selhurst Park; considerably less than ten thousand were rooting for the 'home' team.
The spirit of this friendly match between the Dons and Football Club United of Manchester was one of kinship and even celebration. But, football fans being football fans, the opportunity to get their own back was one that was too irresistible to pass up. The United fans would expect nothing less.
AFC Wimbledon were created in response to the first, and bitterly unwelcome, case of football franchising in the UK. A club run by and for the fans, despite early difficulties, three years on is clearly in the rudest of health - two promotions and the ownership of a 4,500 capacity stadium bears testament to this.
So it is hardly surprising that when those fans of Manchester United who feel their club has been taken away from them (not in the quite literal sense as happened to Wimbledon, but in the erosion of bonds between the club and its supporters, brought into stark focus by the hostile takeover of Malcolm Glazer) decided they too would form their own club, they turned to AFC Wimbledon for inspiration.
In less than two months FC United has been formed and entered into the North-West Counties league, three tiers below that which their hosts on Saturday compete. Still taking tentative steps, it seemed natural that this year's Supporters Direct Cup should be contested between two sides with more in common than just a love of the game and a desire to win.
'This game is one I've been looking forward to ever since the idea of FC United was floated,' wrote Dons chairman Kris Stewart in his programme notes. 'As soon as it became clear that a new club was likely to happen, we made it clear we would love to arrange a friendly. I just hope they enjoy themselves as much as we have.'
United, considering they were playing only their second-ever game, and against an established side from a higher division, held their own for spells with their hastily cobbled together team of ex-pros and kids, largely United fans themselves. AFC Wimbledon, too, were bedding in a number of new players which perhaps explains why it took them an hour to score what proved to be the only goal of the game.
Another reason was Barry George's man-of-the-match performance in the United goal. George, who represents Great Britain's partially-sighted side, pulled off two stupendous stops from close range and fully deserved the award.
Judging from the industry and, at times, ability in the United team they should walk their division next season.
But the result of this game, even the performances, despite both managers' protestations to the contrary, was never high on the list of priorities. It was about one set of fans who've been through the heartache and difficulties of first losing something precious to them and then recreating, from scratch, something to replace it, giving a helping hand to others trying the same; letting them know that, if you want it enough, it can be done.
Of the 3,300 crowd - surely a record for a non-league pre-season friendly and a figure a couple of league clubs would cast covetous eyes at - around 1,000 were from the north west. Noisy and passionate throughout, they were clearly revelling the beginning of this adventure.
'It's not just about Glazer,' John, a season ticket holder at Old Trafford for over 15 years, but no longer, explained. 'This has been coming for years. Keano got it dead right when he had a go at the prawn sandwich brigade. That's all it is now, big business. Me and loads like me have just had enough.'
His travelling companion Kieran agreed: 'They've forgotten that the fans are what are important to a football club. We just want to have fun again. This day was great, even though we didn't win, and fair play to AFC Wimbledon. They've shown what is possible and made us welcome today.'
Over 2,500 fans turned out for FC United's debut match, a creditable nil-nil draw with Conference South side Leigh RMI and that, coupled with a ground share with League Two Bury at Gigg Lane, mean the portents look good.
So much so that manager Karl Marginson has already targeted a league and cup double in the coming season.
'It's all happened so fast,' the former league player with Rotherham United says, 'that we haven't even got a set of nets to train with yet; we're doing shooting practice with slalom poles. But our aim remains to win the league and cup this year. We just want to win every game. That's the way I am as a person. We don't expect to win because you can't expect anything in football but we are quietly confident.'
And what of the significance of the day itself, the support and what United are trying to achieve?
'Personally, I'm a football manager, so I'm just looking at what's happening out on the football field. The fans were absolutely fantastic. Hopefully they'll carry on, keep supporting us so the lads can go out and do the business on the pitch.'
'But if I wasn't the manager,' admits Marginson, 'I'd probably come and watch them myself.
'My lad can't go to Old Trafford now like I used to. I used to go to the Stretford End and sit on the bars to watch United. My lad just can't do that because of the cost. It's all big business. The players' wages need paying and who are the people who end up paying? - the fans. The fans are what's important about a football club and that's been lost now.
'Once we've got a first team up and running we'll be able to get involved in community schemes and re-establish that link.
'I'm a United fan, Phil [Power, the assistant player-manager] is a United fan, most of the lads are United fans and I'll still be looking out for the result. I'll still want them to win but I simply can't afford to go to games anymore. And it's not just United it's happening at, it's all through football.'
But now fans are beginning the slow journey back. Eleven clubs are now either completely owned by fans or have a majority say on the boards of their clubs and the heartbeat of the game is beginning to be heard outside the top flight of the game in this country.
You can only push people so far it would seem - even the prospect of Champions League football and watching the finest home-grown talent in recent years in Wayne Rooney has not proved enough to seduce some of United's most committed fans into paying through the nose for a sanitised atmosphere where they are treated simply as customers rather than the lifeblood of the institution their passion and fervour has help make great.
And any clubs assuming they can exploit their loyal followers with complete impunity would do well to have cast an eye towards West London last weekend. As the late, great Jock Stein - a true football man if ever there was one - famously said: 'Football without fans is nothing.'