If it turns out to have been what many thought it could be before kick-off - a qualification play-off - then what a game it was. For 45 minutes, we purred about an almost perfect Inter that showed it knew how to suffer while being beautifully clinical when chances came. And, when it all unraveled in the face of an unrelenting yellow-and-black tide, it felt like an object lesson in how far the Nerazzurri have come - but also how far they still have to go.
Those of a more optimistic disposition can cling on to a first half where the Serie A side looked about as good as they ever have this season. Since their opening 45 minutes at Camp Nou, in fact.
They soaked up pressure and stung their opponents with two perfectly worked goals. At times, too, they got in Dortmund’s face high up the pitch and looked like they had the tactical balance right against a team which will always give you chances. However, it all came tumbling down in the second half like spaghetti from a packet with a hole snipped in the bottom.
That will be the aspect which Antonio Conte still has to work on most with this side - particularly at a European level. If any coach has made never letting your guard down his watchword then it is probably the former Juve, Chelsea and Italy boss. He would surely have told his troops at the interval not to think the job was done. But instead of going for the jugular, they helped throw their hosts a lifeline.
Two of the comeback goals came from Inter inaccuracies - expertly pounced upon - with the third a sumptuous move which cut the away side open. It is those little distractions which Inter will have to cut out if they want to complete the transformation their new leader craves. You might even get away with these things against some of Serie A’s lesser lights - but you will rarely do so in the Champions League. And defeat was duly delivered, from Borussia with love.
It all means that qualification looks a lot more improbable than it did at half-time in this fixture. It would likely take a couple of favours from Barcelona - and a helping hand from Slavia Prague on the final matchday - for Inter to hope to progress. The pragmatists will say that this team might be better focusing on winning domestically first before letting their heads be turned by Europe anyway. The more cynical will say it shows once again their coach’s deficiencies on the continent.
That would be a little harsh, however, based on this game alone. There was enough hope for the Milanese club to cling on to, despite the painful lessons of defeat. Lautaro Martinez keeps coming on in leaps and bounds, Nicolò Barella looks more complete every time we see him and Stefano Sensi’s return from injury was an immense tonic. Things need not be all doom and gloom.
This was the kind of setback that, one imagines, Conte will use to hammer his message home. Play with the focus and determination you did for half of this match, and we can go a long way. But get distracted for a moment and you can forget any dreams of silverware for another season. In the Westfalenstadion, his new club showed their good and bad sides in the space of one match. It will be up to the players to demonstrate whether this was a lesson they can learn from or an indication of deeper failings which will ultimately undermine their hopes of a trophy.