A trip to managerless Crystal Palace on Saturday might still be a straightforward engagement for Arsenal, but a home defeat in the Champions League when all was going so well introduces a degree of doubt ahead of a demanding month.
Arsenal face successive league games against Liverpool and Manchester United with an away trip to Borussia Dortmund crammed in between. Before that there is a Capital Cup encounter with Chelsea to negotiate. Any night with Jose in the house has the potential to spike stress levels, even though the "Happy One" is threatening to send out the kids.
A feature of Arsenal's early-season gallop has been a fixture quirk that has seen them face only one team in the top half of the table, Spurs. Arsène Wenger has handled the balmy days of late summer with caution, insisting that a proper measure of his team's potential would come at the end of November. Tuesday's 2-1 reverse to Dortmund added significant weight to that position.
Arsenal had become accustomed to dominating engagements. Mesut Özil appeared on the English scene like a player from another planet. His speed of thought and grace of foot was a factor opponents had not encountered when playing Arsenal before. Dortmund knew all about him, and had a plan to counter his influence.
It is fair to assume that the growing Özil dossier at Anfield and Old Trafford will bear similar scrutiny ahead of fixtures that always carry a heightened emotional burden, night time reading for Brendan Rodgers and David Moyes, you might say. By the time Arsenal go to Napoli for the return fixture with Rafa Benitez, the season could have a different complexion.
Wenger conceded that the Dortmund defeat meant his team would have to fashion a win either in Germany or Naples to be sure of progressing into the knockout stages. This is not a scenario he was contemplating after opening with successive wins.
Wenger felt his side were punished for lack of nous not effort or ability. In that he was surely right. You cannot win them all. Dortmund edged the opening half hour on Tuesday and when Arsenal got up a head of steam they were never discomfited. Arsenal had the ball in the net illegitimately in the second half and Santi Cazorla hit a post, but there was never a sense that the visitors were hanging on. And as the winning goal showed, Dortmund were always alert to the half chance.
Victories on the European road by Chelsea and Manchester City demonstrated how two of Arsenal's biggest rivals for honours are settling into a winning rhythm. Both have had uncharacteristic results this season but with each outing appear to be building persuasive momentum.
With Özil contained, Aaron Ramsey pressed back and Jack Wilshere labouring with an ankle that is slow to recover, Arsenal found it harder to create clear openings, and when not in possession, were not as efficient, to use Wenger's favourite word, or disciplined defensively as Dortmund.
The margins are small. Dortmund contested the Champions League final five months ago. They stand only one point behind Bayern Munich at the top of the Bundesliga. Arsenal will not meet many sides this season that combine industry and imagination so brilliantly. The difficulty is that Dortmund showed Arsenal's English rivals how they might be contained.
It remains a measure of any side how well they respond to adversity. Arsenal have been presented with an unwanted invitation to prove their mettle. The fixture list has obliged with a testing sequence that will tell Wenger just where his team stands in the pecking order.
Arsenal's season easy start?
By Saturday at 3pm...
Arsenal will have played the bottom three in the league (Palace, Sunderland and Norwich).
They will have played eight of the bottom 10.
They will only have played Spurs from the top half of the table.