Having been comprehensively defeated 4-0 in the initial leg of the quarter-final, Dortmund, bereft of any further downside on Tuesday, assailed Barcelona from the commencement, thereby disconcerting the visiting contingent.

Barcelona's head tactician, Hansi Flick, a veteran of numerous encounters — and triumphs — against Dortmund during his tenure in the Bundesliga, articulated that the fervid home support necessitated an anticipation of a challenging return fixture, notwithstanding his squad's commanding four-goal aggregate advantage.

Flick conveyed to broadcaster Amazon Prime, "I harboured a degree of premonition that an eventuality of this nature was impending; one is compelled to acknowledge Dortmund's deserving triumph today, having evinced a superlative performance, whilst also extending commendation to my own squad for attaining the semi-final stage."

The usually potent offensive duo of Raphinha and Robert Lewandowski, Barcelona's leading goalscorers in the Champions League this season with 12 and 11 tallies respectively, were uncharacteristically subdued, their most significant contribution being a lacklustre effort from Raphinha that posed minimal threat to Dortmund custodian Gregor Kobel.

"Guirassy serves as Dortmund's veritable 'life insurance'," opined coach Niko Kovac in the wake of a fixture that further underscored his precipitous ascent to prominence and positioned him at the apex of this season's Champions League scoring charts. "Serhou merely requires the unwavering backing of his compatriots on the pitch, a prerequisite for any front-line player, and this he received in ample measure today."

Dortmund's quarterfinal hopes were ostensibly dealt a fatal blow in the initial fixture, further compounded by the eleventh-hour pre-match incapacitation of skipper Emre Can and midfield linchpin Carney Chukwuemeka due to injury.

For a period, Guirassy rendered the seemingly impossible tenable.

Having squandered opportunities in the initial encounter and passed up further chances early in Tuesday's fixture, Guirassy evinced unerring precision from the penalty mark in the eleventh minute following a collision between Barcelona custodian Wojciech Szczesny and Pascal Gross.

Guirassy's header extended the lead to two clear goals in the forty-ninth minute, prior to Ramy Bensebaini's egregious own goal which served to exponentially compound Dortmund's already formidable predicament, stemming from Fermín López's low-driven cross deflecting off Bensebaini's ankle – a denouement of multifaceted chagrin for Dortmund, given the defender's pivotal, indeed indispensable, role in the abortive comeback endeavour, having provided the assist for Guirassy's second successful strike only moments before.

Capitalising on Ronald Araujo's defensive misjudgement, Guirassy secured his treble with a potent, point-blank strike in the seventy-sixth minute, thereby assuming the mantle of the Champions League's premier marksman for the current campaign with a tally of thirteen goals.

This provided Dortmund with renewed impetus in their pursuit of what would have culminated in one of the most storied revivals in Champions League history—a feat comparable to Barcelona's against Paris Saint-Germain in 2017—however, Barcelona ultimately maintained their advantage to advance.

Barcelona finds itself in the semi-finals for the first time since the 2018-19 campaign, poised to confront either Inter Milan or Bayern Munich, whilst Paris Saint-Germain, despite a 3-2 second-leg deficit, secured their berth in the final four through a 5-4 aggregate triumph over Aston Villa in Tuesday's concurrent fixture.

Beyond marking Barcelona's inaugural defeat across all competitive spheres since the 2-1 reverse against Atletico Madrid on December 21st, this outcome represented the club's initial Champions League loss since September, and indeed only the seventh such reverse across Flick's half-century of matches at the helm. Preceding this fixture, the German tactician had heretofore secured an unblemished record of seven victories from as many encounters against Dortmund, garnered during his tenures presiding over both Barcelona and Bayern.

Dortmund's hallowed ground may remain devoid of the Champions League anthem's stirring strains for a considerable duration.

The preceding season's Champions League finalist currently languishes in eighth position in the Bundesliga table, with a mere five fixtures left and a six-point deficit separating them from the coveted Champions League qualification berths.