Sir Alex Ferguson conceded last week that United's away form in the Premier League is the one area he would accept criticism - and once again it has come back to haunt them.
Arsenal's title hopes might still be slim, but they've certainly turned the screw on the Reds.
United – as they have so often done in Europe this season - were able to ditch their poor away league form last Tuesday with their emphatic destruction of Schalke, but mysteriously were once more troubled by the travel demons at the Emirates.
Fergie was pretty dismissive last Friday when a journalist pointed out United's poor record away from Old Trafford against the top sides.
Only two league points from a possible 12 this season against City, Spurs, Chelsea and Liverpool is not great reading, and he thanked the media man sarcastically and with a wry smile.
Seven away points gleaned from the last 18 available since the Invincible bid was shattered at Wolves wasn't impressive either.
But shielding his side from potential confidence-sapping figures is pointless.
No matter the history, United are well capable of playing 'for the moment' - as they did in Gelsenkirchen to set up an almost certain Wembley visit for the Champions League final.
But at the Emirates the Reds saved one of their more quieter days for an occasion when they needed to be at their very best.
It wasn't wise for the Arsenal stadium's announcer to play The Clash's 'London Calling' before the game. They'd done the same in Germany at the Veltins Arena and that certainly inspired United's Champions League bid.
While the climax to the campaign has seen the Reds' resilience turn into panache over recent weeks, Arsenal fans have despaired that once again their side have choked when it really matters.
The Gooners live a roller-coaster life during a game – they admire the brushwork but tear their hair out at the final piece on the canvas.
And this was the Gunners all over yesterday. United could be reasonably content at allowing them possession, knowing they'd self-destruct or the Reds' defence would snuff out that final pass.
The Reds may have been cursing on Saturday watching Chelsea snatch a controversial win against Spurs.
The Reds' nearest league rivals remain in the contest thanks to the goal by Frank Lampard that shouldn't have been.
But you couldn't complain that Carlo Ancelotti has bagged crucial rights on good fortune going into the final weeks of the season after Nemanja Vidic got away with a blatant penalty offence at the Emirates.
Attempting to get a vital touch on Theo Walcott's dangerous cross, the Serb's flailing hand took the ball off Robin van Persie's head.
The Dutchman was livid that both referee Chris Foy and his assistant failed to spot the United captain's touch.
Although it was typical Arsenal – good build-up but no end finish - it was pretty untypical United, who lacked invention and spark. The Reds looked more like early-season stutterers than the slick machine of late.
With nine of the starters from the win over Schalke in Fergie's Emirates line-up - the only alterations being Nani for Valencia and Anderson for flu victim Giggs - perhaps the venture in Gelsenkirchen had taken more out of them than the stroll looked likely to.
United, though, don't get unduly panicked and they probably knew the longer they could keep Arsenal at bay the more likely Arsene Wenger's side would be to lose it.
And there was always a smash and grab potential for the Reds to burst away and clinch the win they desired.
One of their closest chances came just after the interval when Rooney's well flighted free-kick was pawed away desperately by the flying Pole Wojciech Szczesny in the Arsenal goal.
But in the end it was the Gunners who pulled off the smash-and-grab raid.
United's most dangerous spell, consisting of two free-kicks, coincided with the home side carving open the chance their supporters were beginning to believe was impossible.
Van Persie raced away down the right in the 56th minute and had time to stop, look around and pick out Aaron Ramsey.
The Welsh midfielder had the bonus of not being closed down and he seized on the luxury to simply sidefoot home.
United got away with the Vidic penalty incident but it was evened up when substitute Michael Owen was forced into a stumble by the clumsy Clichy as he ran onto an inviting Rooney clip over the top.
You'd have thought the Premier League trophy was about to be presented the way Arsenal fans celebrated at the conclusion.
United might be a touch more concerned now that they won't be the ones enjoying the ticker tape cascade on May 22, unless they can somehow pretend that Ewood Park is Old Trafford in a fortnight.