Wednesday night's amazing last 11 minutes encapsulated all that had gone before as the Londoners trailed to David Villa's early goal and looked fortunate to be escaping with just a 1-0 defeat.
Like a boxer entering the 11th round behind on points, Arsenal landed an equalising punch almost out of nowhere when Robin van Persie fired the ball past Victor Valdes at his near post.
Buoyed by a crowd previously hypnotized into silence by Barcelona's mesmeric passing suddenly screaming feverishly, they then landed the knockout blow with Andrey Arshavin's assured finish to a brilliantly executed 80-metre counterattack.
The victory showed Arsenal that even the toughest nut in world football has a glass chin and they now travel to Spain with belief coursing through their veins.
"We are not favourites and I still believe they are the best team in the world but we know we can beat them - we didn't know that last year," manager Arsene Wenger said after one of the proudest nights of his distinguished career.
"I'm very proud for Arsenal Football Club tonight because everybody urged us to play differently to our nature. We can be proud of the result, but more than pride it can strengthen the belief in our philosophy."
A year ago when the teams met at Emirates stadium in the quarter-finals Barcelona were arguably even more dominant in the first half, yet failed to score.
They did race into a 2-0 lead early in the second half but, just as on Wednesday, they sat back to admire their own handiwork and allowed Arsenal to scramble a 2-2 draw.
After 20 minutes of the second leg, having been given the runaround for the best part of 110 minutes of action, Arsenal were, against all logic, actually leading the tie after Nicklas Bendtner put them ahead in Spain.
For all the marvelous inter-play of a side who provide the bulk of Spain's World Cup-winning team, it fell to Argentine striker Lionel Messi to turn the contest with a brilliant night of individual class as he rattled in four goals to secure a 6-3 aggregate win.
Arsenal are unlikely to implode again as they did then and Wednesday's experience of being largely out-passed on their own ground yet still winning puts them in a healthy state of mind for the second leg.
Barcelona's ice-cool coach Pep Guardiola did not seem overly concerned after the game but, having been dumped out by Inter Milan last season when his team had seemed nailed on for the title, Arsenal have at least succeeded in sowing another seed of doubt.
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