It was the fifth round in February 2008 and they sat on top of the Premier League table, five points clear of second-placed United. Their form was superb.
Wenger, though, took the decision to shuffle his pack and history would judge him harshly. In came the inexperienced full-backs Justin Hoyte and Armand Traore while Emmanuel Eboue played in midfield as Mathieu Flamini was rested and Nicklas Bendtner started ahead of Emmanuel Adebayor up front. The Gunners were thrashed 4-0 and they lost their heads, as well. Eboue was sent off for a bad tackle on Patrice Evra and William Gallas was fortunate to escape punishment for kicking out at Nani.
The statistics for Arsenal after the humiliation at Old Trafford retain the capacity to make their supporters wince. They won only one of their next eight Premier League fixtures, drawing five and losing two. Their title challenge turned to dust. In the Champions League, meanwhile, after getting past Milan, they were beaten by Liverpool. Their season was over by the middle of April. United would win the Premier and Champions Leagues.
The FA Cup tie at United was the weekend before the notorious league game at Birmingham City, when Eduardo broke his leg and Arsenal threw away two points in the last minute, prompting Gallas to throw his strop. But if St Andrews is commonly acknowledged as the scene of Arsenal's unravelling, the impact of Old Trafford should not be underestimated. "I do not pretend I get every single decision in my career right," Wenger said, as he reflected on his team selection that day and he considered the one for this season's FA Cup quarter-final with United at Old Trafford. The manager will not make the same mistakes again, although the circumstances surrounding this tie are different. There is the clear parallel in that Arsenal are once more locked in a championship fight with United but they travel to the north-west with their morale in tatters and the feeling that they are being persecuted, variously, by the Fates, referees and Uefa.
The cynic might suggest that their unravelling has begun already as the past two weeks have brought Carling Cup final calamity against Birmingham, Premier League frustration against Sunderland and Champions League anger and anguish against Barcelona. Defeat at Old Trafford would see a third route to silverware blocked off and it would surely have psychological consequences in the bigger battle with United for the title.
Wenger pointed out that United had also suffered dispiriting defeats, at Chelsea and Liverpool in the Premier League, while his opposite number, Sir Alex Ferguson, might pick his team with an eye on Tuesday night's Champions League last-16 second-leg tie at home to Marseille. Wenger, though, is exercised purely by what he and his players have to do.
"I'll play my strongest team," said Wenger. "My intention is always to put out a strong team who I believe have a good chance to play. Ourselves and United are two teams with disappointing results recently and it is about who deals the best with that. We need it [a psychological boost], I must say, because we need help. We have been touched severely recently and we are chasing a win of this type. We want to deal well with the psychological blows we have had. That's our purpose."
The renewal of championship hostilities between Wenger and Ferguson has brought to mind many of the classic encounters between the pair. For the record, Wenger's favourite was Arsenal's 1-0 win at Old Trafford in 2002 that secured the title for them, while his worst was Pizzagate, the 2-0 away defeat in 2004 that ended his team's 49-match unbeaten record in the league.
That was sparked by the award of a controversial penalty, which was converted by Ruud van Nistelrooy, and Wenger highlighted how United had been given five penalties against his team at Old Trafford in the last seven and a half years. The state of the pitch was another beef. "It's never perfect there," he said. "They have to relay it a lot and, sometimes, the joins are not together."
Wenger's challenge is to plot a course past opponents he feels have been cagey against his team. The Arsenal winger Samir Nasri bemoaned United's use of "three defensive midfielders" against them at Old Trafford last December, in the Premier League fixture that United won 1-0, and he suggested they had been "scared" of Arsenal.
"United always play against us with three tight in midfield," Wenger said. "They played only Wayne Rooney up front [in December], so I think they always set up against us to defend well. I wouldn't say they are scared but they always have a realistic approach to the game. Our problem will be not to be caught in midfield and maybe to attack on the flanks." Wenger's biggest problem would be another defeat.
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