Having suffered a 4-0 thrashing in the initial leg of the quarterfinal, Dortmund, facing an insurmountable deficit on Tuesday, eschewed caution and assailed Barcelona from the outset, thereby destabilising the visiting side.

Barcelona manager Hansi Flick, well-versed in confronting — and indeed conquering — Dortmund from his Bundesliga tenure, acknowledged that the fervid home support had led him to anticipate a formidable second leg, notwithstanding his squad's four-goal aggregate advantage.

"A nascent apprehension regarding such an eventuality had been subtly brewing within me," Flick confided to the broadcaster Amazon Prime. "On this particular occasion, one must extend felicitations to Dortmund, for their performance was unequivocally commendable, and likewise, congratulations are due to my own squad, as they have secured their place in the semi-finals."

In an atypical turn of events for Barcelona's usually formidable attacking duo, Raphinha and Robert Lewandowski – who boasted twelve and eleven Champions League goals this season, respectively – remained notably subdued, with Raphinha's rather insipid attempt at Gregor Kobel the closest either came to breaching the Dortmund net.

Guirassy serves as Dortmund's "sine qua non," opined coach Niko Kovac post-match, a fixture that further cemented his meteoric ascent and installed him as the leading scorer in the Champions League this term. "Serhou's efficacy is contingent upon the unwavering corroboration of his peers, an imperative for any striker, and such a confluence of support was duly afforded him this very day."

Dortmund's quarterfinal fate was arguably sealed in the initial leg, further exacerbated by the pre-match declaration of captain Emre Can and midfielder Carney Chukwuemeka as hors de combat due to injuries.

For a period, Guirassy rendered the ostensibly unattainable seemingly viable.

Having squandered opportunities in the initial leg and subsequently let slip two further chances in the early stages of Tuesday's encounter, Guirassy demonstrated unerring accuracy from the penalty spot in the eleventh minute, capitalising on the collision between Barcelona custodian Wojciech Szczesny and Pascal Gross.

Guirassy's header extending the lead to 2-0 in the forty-ninth minute preceded a calamitous own goal from Ramy Bensebaini, which compounded Dortmund's predicament, López's low cross inadvertently deflected off Bensebaini's ankle—a double indemnity for Dortmund given the defender's pivotal role in their attempted revival, having recently supplied the assist for Guirassy's second.

Guirassy capitalised on Ronald Araujo's defensive miscue, completing his treble with a potent close-range strike in the 76th minute, thereby ascending to the pinnacle of this season's Champions League goal-scorers with a tally of 13.

The goal reignited dormant hopes within Dortmund of engineering what would have been a comeback of near-mythic proportions in the annals of the Champions League – one potentially eclipsing even Barcelona's celebrated overturning of Paris Saint-Germain in 2017 – although Barcelona ultimately evinced sufficient mettle to secure their passage.

Barcelona is poised to contend with either Inter Milan or Bayern Munich in the forthcoming semifinals, marking their initial advancement to the Champions League's penultimate stage since the 2018-19 campaign. Concurrently, in the other quarterfinal encounter on Tuesday, PSG secured their berth in the semifinals via a 5-4 aggregate triumph over Aston Villa, notwithstanding their defeat in the second leg by a margin of 3-2.

Beyond marking Barcelona's inaugural defeat across all competitive tiers since their 2-1 reverse against Atlético Madrid on December 21, this setback constituted their premier UEFA Champions League capitulation since September and a mere seventh in Julian Nagelsmann's quinquagenarian tenure at the helm, the German strategist having hitherto triumphed in all seven of his prior encounters with Borussia Dortmund during his stewardship of both Barcelona and Bayern Munich.

Dortmund may find themselves in a protracted hiatus before the stirring strains of the UEFA Champions League anthem once again resonate within the hallowed confines of their stadium.

The preceding season's Champions League finalist languishes in eighth place in the Bundesliga with five fixtures remaining, trailing by six points the quartet of coveted Champions League qualification spots.