Their defensive issues were obvious, Fabian Delph and Gabriel Agbonlahor causing problem after problem by running at the heart of the defence. If they looked that shaky against Villa, you thought, how on earth would they fare against the top sides?
It's to Arsenal's credit that they recovered enough from that start to assume their familiar position in the top four and to remain in the title race as long as they did, but the problems were never solved, they were merely disguised, as that record of 17 goals conceded in three away games against Manchester City, Liverpool and Chelsea demonstrates.
Per Mertesacker and Laurent Koscielny are both fine defenders, as they showed in a resilient display away to Tottenham, but what they are good at is dealing with crosses.
Neither is naturally quick and neither is nimble; both struggle against opponents who run at them. What Arsenal have managed to do for much of the season is to protect the space in front of them, preventing opponents ever getting a clear run at them.
Mikel Arteta was key to that, as was Aaron Ramsey, whose injury has proved extremely costly, while Mathieu Flamini added such steel that there is a reasonable argument that he has proved a more effective signing this season than Mesut Ozil.
The oddity is that Flamini has fallen from favour in recent weeks, so he didn't start the away leg against Bayern Munich, or the league games at Tottenham and Chelsea.
Yet the facts are stark: Of league games in which Flamini has played more than 45 minutes, Arsenal have won 12, drawn two and lost only the away match at Manchester City (although he was on the pitch for City's first four goals in Arsenal's 6-3 defeat).
Of games in which Flamini has played fewer than 45 minutes, Arsenal have won seven, drawn four and lost five. He did not play in the 5-1 defeat away to Liverpool because of suspension and was omitted from the starting line-up at Stamford Bridge as part of Arsene Wenger's experiment with a new shape in midfield.
Rather than the 4-2-3-1 that has been the default for most of the season, away to Bayern, Tottenham and Chelsea, Wenger has preferred to have Arteta flanked by Alex Oxlade-Chamberlain and Santi Cazorla.
In the first two of those three games, it was a shape that seemed to suit Oxlade-Chamberlain, who caused problems surging forwards from deep. The rationale for the change, though, still wasn't entirely clear: Taking out a tackler for two more creative players would be logical if the aim was to use the ball better or have better control of possession, but against Bayern, Arsenal had just 33 percent possession and against Spurs just 41 percent.
If anything, by leaving Olivier Giroud isolated, the formation seemed to invite pressure.
Chelsea not merely applied pressure, they also pressed with great vehemence, at least in the early stages until the game was won."We came to kill," said a gleeful Jose Mourinho. "And we crushed them."
He went on to detail how vulnerable Arsenal were if a side could close them down quickly at the back, preventing them slowly building up play.
Oxlade-Chamberlain gave the ball away for the first and Cazorla for the second; in fact, the first five Chelsea goals came from Arsenal surrendering possession cheaply, an issue that was part tactical and part a result of what the Daily Telegraph journalist Paul Hayward termed "a conviction deficit;" Arsenal seem to have simply stopped believing they can win the biggest games.
Worse, having conceded possession, the new shape meant there was no cover for Mertesacker and Koscielny, while Lukas Podolski offered Kieran Gibbs little protection.
Everything was too stretched; there was none of the compactness most modern managers demand. Chelsea, the most adept team on the counter in the Premier League, were able to surge through at will.
What happened at Stamford Bridge was a failure of both mentality and tactics—and what's really damning is that it didn't come as a surprise.
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