With a few minutes of normal time remaining, a roar of joy and relief swept across the Westfalenstadion. For the twenty odd minutes before that, and after Julian Brandt had given them a 2-1 lead over eliminated Slavia Prague, Borussia Dortmund's Champions League hopes were in the balance.

That noise wasn't generated by the men in yellow and black on the field but by a 17-year-old in a Barcelona shirt almost 100 kilometers away in Milan. Ansu Fati's superb strike had just put Barcelona 2-1 up against Inter Milan, which meant that Dortmund had breathing space. The goal that the Czech side had been threatening was no longer relevant. Lucien Favre's side were all but through.

The celebrations were understandable; this was arguably the toughest group in this year's competition and Slavia are still the only side to have stopped Barca winning at the Camp Nou this season. But with second place meaning Dortmund will play Paris Saint-Germain, Manchester City, Juventus, Liverpool or Valencia, questions will eventually have to be asked about whether it makes any real difference.

On the evidence of Tuesday night, probably not. The Bundesliga side started well and could have been out of sight had Marco Reus' composure not deserted him once again. The Dortmund captain had squared for Jadon Sancho to open the scoring in the 10th minute, but couldn't put his own name on the scoresheet. The chances continued to come but not just for the home side. The Czech First League leaders forced Roman Bürki in to a brilliant, one-handed grasping save from a grounded position before Tomas Soucek burst on to a knockdown from a cross to beat Dortmund's static centerbacks to the ball and fire home.

After the break, Dortmund started once again to demonstrate the attacking qualities which are rarely in doubt, with Julian Brandt collecting an intelligent and measured Sancho through ball to lash in at the front post just after the hour mark. With Inter level at that point, BVB were heading through to the last 16, a stage they've only been past once since 2014, when Jürgen Klopp was at the helm.

Then came the sort of defensive jitters that are fast becoming part of the club's identity. Bürki made three more smart stops while Prague contrived to miss a set-piece chance from inches out. "Roman made five, six, seven world-class saves today," Mats Hummels told DAZN afterwards. Suddenly every ball in to the box was causing panic while, at the other end, Sancho and Thorgan Hazard both passed up chances to take some pressure off their creaking backline.

Fati's strike in the San Siro did the job for them, but this was not a Dortmund display that will strike much fear in to any of their potential opponents. 

Julian Weigl's late sending off after two bookings in 11 minutes was one of a number of nervy signs from a team who have struggled to consistently win comfortably. There seems no easy fix either. Mats Hummels, after a strong start, is starting to validate Joachim Löw and Bayern Munich's theory of decline, Manuel Akanji has regressed, Nico Schulz looks lost after his move from Hoffenheim and Achraf Hakimi is always more comfortable on the front foot.

But there are also structural and tactical issues that Favre and the board haven't quite solved. Did Dortmund really need both Hazard and Brandt? What's the plan to protect the back four when Axel Witsel, injured until at least the new year, isn't there? Can Weigl do the defensive dirty work well enough? Can Thomas Delaney find form again?

In European terms, Favre has a little while, and the club have a transfer window, to come up with a more convincing set of answers before the knockout ties in February. Get past one of those teams and the celebrations will truly be earnt.