As Gregor Kobel made an inspired save to his right to save Riyad Mahrez's 58th minute penalty, Manchester City coach Pep Guardiola must have wished he hadn't taken Erling Haaland off at half-time.

On his return to Dortmund, Haaland had made little impression in the 45 minutes that he was given. But Haaland and City had been kept at bay by a Dortmund side that discovered a side to their game that has often been absent in this, yet another so-called transition season.

"We did a good job of keeping the ball away from our goal, and that's where Erling Haaland operates. So we're happy he only played for 45 minutes tonight," Dortmund's Jude Bellingham told Amazon Prime after the game.

Kobel added: "We were disciplined and compact defensively and we deserved it tonight."

'Sexy football, back heels and flicks'

Mats Hummels, commanding alongside Nico Schlotterbeck and deserving of his man of the match award, had called on Dortmund to do more of the ugly side of the game after the 1-1 draw against Sevilla two weeks ago, Dortmund's last outing in the Champions League.

"We need to get it out of our heads that successful football has to be sexy football, all back-heels, flicks and one-two-three in five-yard spaces," criticized the former Germany defender. "We must have lost the ball about 20 times totally unnecessarily, we kept trying to play in tight areas rather than making the opposition run."

The veteran defender's criticism proved to be prophetic when, five days later, 20-year-old Adeyemi's attempted back-heel flick on the half-way line resulted in Union Berlin winning possession and breaking away to go 2-0 up. 

"Sometimes, a 20-yard back-pass is the best solution, even if it doesn't make it on to social media," said Hummels afterwards. "It's so important in football to know when risk is appropriate and when it's not. But knowing when to try a trick and when not to is an issue we've been having for over three years now."

Dortmund coach Edin Terzic concurred following the defeat in Berlin, concluding: "Are we prepared to do the things which we don't enjoy doing? They're the issues we have to deal with."

Adeyemi's ingenuity and pragmatism

This was the performance of a Dortmund team that had taken Hummels' words on board. Dortmund delivered on the things that don't make it onto social media, preventing City from establishing a rhythm and reaching their slick best.

Adeyemi's crunching tackle in front of the Südtribüne just before half-time not only stopped Joao Cancelo in his tracks, but showed that this young talent can match his flair with the ball with a necessary amount of pragmatism. The Südtribüne loved it, not least because it was a culmination of Adeyemi's 45-minute tormenting of the Portuguese, who joined Haaland as an onlooker for the second half.

In truth, Cancelo had been tied in knots by the the young German. In the 36th minute, Adeyemi arced his run to perfection, leaving Cancelo for dead and delivering a low cross from which Youssoufa Moukoko should have at least tested City keeper Stefan Ortega, making a rare start since his move to England from Arminia Bielefeld.

Kobel's moment of redemption

City offered more as an attacking force as the contest wore on with Dortmund forced into an energy-sapping display of grit. All the hard work threatened to count for nothing when Emre Can's tired tackle on Mahrez left the referee with no choice but to award a penalty — but it was one that Kobel saved superbly from the Algerian after Dortmund's Gio Reyna has advised him which way to dive.

Kobel's save, a personal moment of redemption following his role in the team's recent defeat by Union Berlin, was symbolic of Dortmund's newfound fortitude. But there's one player who has been demonstrating that every week since he arrived in Dortmund.

"It always feels rewarding when we play like that and defend like that,” said Bellingham, whom Guardiola described as being "something special in terms of his mentality" ahead of the contest.

"It means a lot to get to the next round, we don't take it for granted, and last season was one of my lowest points when we didn't qualify,” the Englishman added.

For this young team to mature together, everyone in black and yellow will be required to demonstrate the same commitment to the dirty work that Bellingham does on a consistent basis. In that regard, this performance offered hope.