For the last 10 minutes of a 2-1 that felt like an 8-2, the visiting fans kept up an unbroken chant of "We love you, Arsenal". Long before that impressive display of solidarity, however, they had supplied ample proof of an anger provoked by the way yet another season threatens to disintegrate in a welter of complaint and recrimination.

As goals from Robin van Persie and Patrice Evra sent Manchester United to the top of the table for the first time this season, after 10 matches Arsenal are already nine points behind the leaders, lying sixth and appearing destined to be caught up in a battle for the final Champions League qualifying position.

Not that the away supporters deserved much sympathy. The vileness of the sustained chants directed at Van Persie made a mockery of Arsène Wenger's pre-match request for a civilised response to the appearance of their former hero in new colours and of his subsequent claim. "They expressed their disappointment because they love Robin – I don't think they were disrespectful," he said. "They've shown more than they're disappointed that he joined Man United."

If anybody wanted to see the evidence that persuaded Van Persie to move from the Emirates to Old Trafford, it was on show in the flaccid, error-strewn performance by an underpowered Arsenal team containing too many players seemingly destined to make no positive impact on the club's history.

It started at the back, with the third-minute error by the captain, Thomas Vermaelen, that invited Van Persie to open the scoring. By delivering a savage blow to Arsenal's morale while encouraging their opponents to slip into a careless, overconfident mode, it was a moment that shaped the course of the entire match.

"We were poor today defensively, I think," Wenger said. "There's no obvious reason apart from the fact that we didn't start well and that Man United have quality up front. They score goals against anybody and they're better than us, as simple as that."

But Wenger gave his opponents a head start by selecting André Santos at left-back, ensuring that Antonio Valencia and Rafael da Silva would have all the space they needed – starting in that third minute, when they combined to give Vermaelen the opportunity to make his catastrophic miskick.

Arsenal supporters were encouraged at the start of the season by the promotion of Steve Bould to the role of Wenger's assistant, with special responsibility for defensive matters. But it is hard to believe that Bould, a revered member of the defence Wenger inherited on his arrival at the club 16 years ago, sees Santos as a satisfactory replacement for the injured Kieran Gibbs. Retaining Carl Jenkinson, the young Englishman, at right-back, where he had played every previous game this season, and bringing Bacary Sagna – returning from injury – back in on the opposite flank would surely have been a better option.

Almost anything would have been better than Santos, and one could only imagine that Lukas Podolski's failure to lend the hapless Brazilian much support on the left flank was the product of a desire to avoid being tainted by association. All that needs to be added is that when Santos bizarrely asked Van Persie for his shirt on their way to the tunnel at half-time, the Dutchman did not bother to ask for his former team-mate's in return.

When Wenger pointed out that their early-season programme had included difficult visits to Stoke, Liverpool and the two Manchester clubs, he was deserving of no more than limited sympathy. Nothing exemplified what appears to be the loosening of his grip than the contrast between his handling of Jack Wilshere and the way Sir Alex Ferguson dealt with Tom Cleverley.

A chance to compare and contrast the two vastly promising young England midfielders was one of the attractions of the encounter. Some people fail to see the point of Cleverley but he was neat and industrious alongside Michael Carrick at the base of United's midfield, while Wilshere, making his second league start after his long absence, showed his familiar ability to accept the ball on the half-turn and move it along with adroitness and relevance.

But after collecting yellow cards in the first half – Wilshere for going through on Cleverley, the United player for a foul on Santi Cazorla – both men were warned after the interval, Wilshere for upending Van Persie and Cleverley for bringing down Wilshere. Three minutes after Cleverley had received Mike Dean's final warning, Ferguson replaced him with Anderson. Wilshere, however, was left on the pitch for the 15 minutes it took him to crunch into Evra as the Frenchman tried to halt his dribble.

"The red card was very harsh," Wenger said. "I find the referees very naive because when you say to the players, 'Look for the next foul and you'll get a second yellow', that means a signal for everybody of the other team to dive. And of course they do it. He went for the ball and Evra made the maximum of it. To me it looked a regular challenge." Not to many others.

Wenger had an excuse for his failure to withdraw a player who, still finding his way back into the rhythms of competitive football, could have been expected to be half a yard off the pace and mistiming the occasional challenge. "We were in a position where we had to attack and I had no offensive midfielders, central midfielders, on the bench," he said. "So I thought I'd leave him a bit longer."

Surely it would have been better to contest the final portion of the match with 11 players, even if one of them was the defensive midfielder Francis Coquelin, rather than run the risk of losing Wilshere and going down to 10 men against manifestly superior opponents. While the narrowness of the eventual scoreline was no more than a trick of the light, the deficiencies in the way the Arsenal squad is currently being managed were glaringly exposed.

Man of the match Vito Mannone (Arsenal)