Robin van Persie sounds death knell for once rich rivalry between Arsenal and Manchester United

Striker has widened the gap between old club and United before Sunday's meeting

Robin van Persie celebrates one of his goals during the title-clinching win over Aston Villa (Getty Images)

Sir Alex Ferguson was heady on the early sensations of having ground Manchester City into the dust and surely did not intend to betray the confidence of a telephone call between himself and Arsène Wenger. But that is what crept out in the brief, fascinating press conference that he broke with routine to give at Old Trafford late on Monday night. Reflecting on Robin van Persie's impact – as great as any player he has signed, he says – Ferguson declared: "Arsène said to me when we concluded the deal: 'He's a better player than you think.'"

What a hammer blow that sentence must have been to Arsenal supporters who read it this morning. As if it was not bad enough that Van Persie's signature goal had revealed United's gain and their own loss to a club they would not cede an inch to a decade ago. Then, Wenger hollered that they did not deserve the 2003 Premier League title and his Arsenal team promptly romped to the 2004 issue. Today, the world was learning Wenger knew there was even more than we imagined in this player and still allowed him to go.

Arsenal fans have been confronted by the unsettling narrative of last summer's Ferguson/Wenger phone exchanges for about six months now. Ferguson mentioned them first, shrewdly wrapping the talk up in flattery of Wenger doing "a phenomenal job getting top dollar" for his erstwhile captain. Then Wenger described the tone. "It was a very professional phone call, and there was more than one," he said. "I will tell you the rest another day..."

"The rest" is a story that defines the difference between the two men. There is Wenger, the arch-analyst who has always been armed with statistics to back up his case when it comes to selling players and who, after bearing witness to some very long, agonising hours of deliberation in the Emirates boardroom – hearing others weighing up the financial metrics in wages lost and income gained of selling Van Persie as if it were some algebra puzzle – agreed to sell. And there is Ferguson, capable of analysis like the best of them but, at heart, a man who operates on the principles of bare football instinct and sheer ruthlessness. He stripped it all away in that press conference on Monday, when saying of the Van Persie deal that "when a great player became available and you feel United should have him, you have to go for him".

Wenger has the gambler's instinct, which the journalist Philippe Auclair has touched upon, though it is a way of living: "a passionate desire to live life to the full, bordering on recklessness," as Auclair has described it. We see the same characteristic in the way he often concentrates on his own team, rather more than tactical consideration of the opposition. But Ferguson knows when to gamble on a player. What a punt that was, last summer – to lay out a £25m fee and £15m a year in wages on a 29-year-old who has had his share of injury trouble. It could have been a monumental disaster.

Arsenal's decision to let United take him conforms to the way they view themselves in the new Premier League landscape. They are defenders, with United, of the old creed of financial sustainability, against the encroachment of the nouveaux Chelsea and Manchester City. Arsenal do not mind being second best, so long as that means second best to United – the only club in England who generate more money than them. United have fought the "financial doping" that Wenger rails about, too – only better, more ruthlessly, always refusing to yield.

The metaphors for Arsenal's timidity will be resplendent when United arrive at the Emirates as champions, this weekend – with the Arsenal players planning a guard of honour for Van Persie and Co. Forgive Arsenal's supporters for approaching this occasion with a knot in their stomachs. None need reminding that the motif of their side's shocking capitulation in the Old Trafford match of 3 November – a 2-1 win for United – was Andre Santos asking for, and getting, Van Persie's shirt at half-time. It was an act that left one former Arsenal and England striker to reflect that Ferguson would never tolerate that kind of act, while Wenger always would. Less noticed was the cuckolded Wenger's warm embrace for Van Persie, who had taken three minutes to put United ahead, as the teams left the field at half-time.

Chants of "Ivan Gazidis, what the f*** do you do?" formed the background noise that lunchtime but more shocking than Santos' actions was an interview with Wenger in January, when he declared that he did not find it painful to watch Van Persie delivering decisively. "But what is painful is to see United so far in front of us. We knew when we sold him to United that would be the case."

Matter of honour

Arsenal are expected to provide new Premier League champions Manchester United with a guard of honour ahead of Sunday's match at the Emirates Stadium. Tradition has seen champions clapped on to the pitch in the past, with United having done so for Chelsea in 2005 and also Arsenal back in 1991 at Highbury.