Suddenly, the arguments against Arsenal as realistic contenders for silverware look very weak indeed.
On Thursday morning (Singapore time), in front of the massed ranks of the WestfalenStadion, the Gunners did something very few teams have done since the arrival of Juergen Klopp in 2008, and shot down Borussia Dortmund.
A victory over struggling Marseille at The Emirates in three weeks may now be enough to secure qualification for the next round.
Dortmund, by contrast, must beat Napoli and the French side to survive. This is not the way anyone expected this group to pan out.
Klopp himself was moved to suggest that Arsenal could now go all the way and win the Champions League, albeit on condition that they avoided Bayern Munich. Arsene Wenger, too wise to get over-excited, made no such prediction, but there was no hiding his satisfaction.
This was arguably his best result since the FA Cup win of 2005. Not only are his team capable of blistering attacking moves, as they demonstrated on Liverpool last weekend, but they can press their backs against the wall and fend off one of the best teams in Europe.
Manchester United, who host the Gunners on Sunday, must take note.
One chance, one goal
This result was all the more impressive for the manner in which it arrived. Arsenal's goal was their first serious attempt on goal, the product of Olivier Giroud's corkscrew neck and Aaron Ramsey's unerring eye for the target.
Dortmund, so devastating on the attack, will rue the shortcomings in their defence. Ramsey could have doubled the lead moments later, denied by the desperate lunge of Roman Weidenfeller. Those chances aside, it was all one-way traffic.
Before and after the Welshman's 11th strike of the season, Arsenal held their lines with a poise and defiance that is fast becoming their style. Per Mertesacker and Laurent Koscielny were utterly indomitable at the back.
In the first half, the towering German pickpocketed a rampaging Marco Reus with such grace that the Dortmund man didn't even realise he no longer had the ball. Behind the defence, Wojciech Szczesny dealt with whatever passed through their deflector shield.
In the centre, Mikel Arteta rode his luck with the referee, but marshalled the middle with real composure, an attribute that is essential when dealing with a team like Dortmund.
Klopp was frustrated with the result and no wonder. His team did very little wrong.
They played in their standard style, holding the ball and then breaking hard and fast.
The way this team pass and move, advancing so swiftly up the pitch, is impossible not to admire, but their destination was always the same.