And significant, really, is the only word for it. From 1997 to 2004, nobody broke the Sir Alex Ferguson/Arsene Wenger-led duopoly that dominated the Premier League title race. Nobody, in real terms, even came close.
"If you look at our history prior to Jose Mourinho's arrival at Chelsea, there was no consistent threat to our dominance outside of Arsenal," wrote Ferguson in his recent autobiography. Alongside the Portuguese, Wenger is the only other manager afforded a chapter to himself in the book.
Yet it was more than just two great teams under two great managers playing two distinctive and nonetheless still brilliant styles of soccer. It mattered. We cared because, so clearly, they did.
From only six months into Wenger's tenure in north London, when Ferguson described the Frenchman as a "novice" to, well, just a couple weeks ago and the release of the former United boss' book, in which he criticizes, among other things, the Arsenal man's ability to produce his own players, it was a rivalry that brought the best and, more enthrallingly, the worst out of both clubs.
The soap opera-style, up-and-at-'em nadir came at Old Trafford 10 years ago, in a game that Sky's Martin Tyler described at the time as "for 75 minutes a football match and then it became a feud." Or, for the headline writers ever since: The Battle of Old Trafford.
It will forever be weaved into the English soccer tapestry. Martin Keown, arms outstretched and neck veins on the precipice of popping, jumping at and onto Ruud van Nistelrooy after the Dutchman missed a penalty that was to be the last kick of a 0-0 draw.
And then all hell broke loose. Gary Neville pushed Keown, Lauren pushed Ryan Giggs, Cristiano Ronaldo pushed Lauren and repeat ad infinitum. It was a cartoon dust cloud short of a full-on brawl and, save for the FA disciplinary panel, which fined Arsenal and number of players from both sides upwards of 275,000 pounds, we loved it. Again, we cared.
Eight months later and Arsenal were The Invincibles. The unbeaten Premier League champions. Wenger's third and, at the time of writing, last league title.
In the following 2004-05 season, United stopped the Gunners from making it 50 games unbeaten in the league, at the cost of Ferguson's suit, which was ruined by a slice of Hawaiian pizza flung by a teenage Cesc Fabregas during another post-match brawl in an image so brilliant that you are almost glad that it never found its way onto the TV cameras.
The game at Highbury that season was also won by United after Roy Keane – the 5-foot-10 Roy Keane – challenged Patrick Vieira (6 feet 4 inches) to pick on someone his own size in the tunnel ahead of the match, after the Frenchman allegedly provoked Gary Neville.
But by then had come the shift - or Mourinho, as he is otherwise known. His Chelsea side embarrassed the warring pair from north London and Manchester and had its first title in 50 years wrapped up by April. And as the Keanes, Keowns and Vieiras quietly drifted away, the venom soon followed.
The old enemies have not ever really been the same since. Wenger's side, consigned to the relative tundra of fourth and occasionally third place since 2005, became by and large an afterthought for a United side preoccupied by the new-monied Chelsea and Manchester City. Over the last five years, Arsenal has finished on average 15 points behind the club which, for the best part of a decade, it dominated alongside and battled against.
It all became a bit ... nice. Wenger or his then-assistant, Pat Rice, returned to Ferguson's office after matches between the two for wine and a chat and the Scot spoke of his sympathy for his opposite number after United systematically blew the Gunners to pieces in an 8-2 battering at Old Trafford in 2011. Even United's signing of Robin van Persie – surely the most significant transfer between two English clubs in more than a decade - was met amicably by an Arsenal outfit resigned to the fact that it had indeed fallen behind.
But it is back. Unquestionably so. A win at Old Trafford for Wenger's side on Sunday would see Arsenal move 11 points clear of their hosts after as many games. It would not only be unprecedented, it is almost unthinkable. Yet a win at Borussia Dortmund on Wednesday and the five-point gap at the top of the table upon which Arsenal currently sits, coupled with the fact that David Moyes has not yet beaten a team currently placed higher than 13th in the league, gives the game an unusual air of role reversal. United is in dangerous territory of being left behind.
And so once more to that word, 'significant,' and to a fixture that had for too long felt anything but. Manchester United vs. Arsenal is now again on top billing. The Battle of Old Trafford is back.