Diego Simeone sank to his knees, then collapsed face-first in his technical area. Even after 674 games at the helm, his Atletico Madrid side still managed to catch him off guard.

He had forewarned of potential struggles in the lead-up; he had cautioned about looming repercussions, emphasizing the necessity for old-fashioned resilience if Atletico, aiming for their first Champions League semi-final appearance in seven years, were to progress.

But resilience was conspicuously absent. What unfolded was sheer chaos. And chaos isn't synonymous with Diego Simeone's style; it's not what defines his Atletico Madrid anymore. No longer the stalwarts of defense. No longer an impregnable fortress. They've shown vulnerability, and Dortmund capitalized on it.

Four times Jan Oblak retrieved the ball from his net. That marked 11 consecutive games without a clean sheet for Atletico Madrid. Dortmund departed Spain after the initial leg trailing 2-1, regretting missed opportunities, having only sparked to life after conceding. Julian Brandt came close to equalizing late at the Wanda Metropolitano - the memory lingered as they entered Signal Iduna Park. At home, it was all about tapping into the fervor of their renowned ‘Yellow Wall’ and setting the tone from the outset, as youth triumphed over experience. It mirrored their overpowering of PSV Eindhoven in the previous round. Amidst the deafening roar, even seasoned teams like Atletico falter.

Hours prior to kickoff, as tradition dictated, the Yellow Wall swarmed with fervent supporters. The visiting contingent responded vociferously, yet Dortmund's players knew they only needed to fan the flames to incite their fans into a frenzy.

They should have seized a 1-0 lead within four minutes, when Marcel Sabitzer, formerly on loan at Manchester United, found himself five yards from goal with a cutback, but hesitated, squandering the opportunity.

Moments later, Atletico countered swiftly, transitioning from defense to attack as they've often done successfully under Simeone, with Alvaro Morata racing through one-on-one. He chipped the goalkeeper, Gregor Kobel, but missed the target. Simeone's disbelief was palpable.

Thereafter, Dortmund asserted dominance, with Brandt, the standout performer, drawing them level before Chelsea loanee Ian Maatsen notched his maiden Champions League goal to put them ahead. Unfancied in the group stage draw alongside PSG, Newcastle, and AC Milan, Dortmund thrived at home, extending their unbeaten run to 10 Champions League games on their own turf. Yet, amidst the inconsistency that plagued both sides' seasons, surprises were perhaps inevitable.

A triple substitution by Simeone at halftime momentarily altered the course of the game, as an own goal by Hummels and a composed finish by Angel Correa put Dortmund's progress in doubt.

However, Atletico's resurgence proved short-lived, as Niklas Fullkrug and Sabitzer struck in a three-minute frenzy. Simeone was left perplexed.

"Dortmund’s official account tweeted a string of characters," signifying their goal. It was as nonsensical as the football on display. Pure chaos, pure drama. Everything Atletico Madrid haven't been at their best under Simeone.