Having suffered a resounding 4-0 defeat in the initial leg of the quarter-final tie, Borussia Dortmund, confronting a seemingly insurmountable deficit on Tuesday, adopted an unequivocally offensive posture from the outset, thereby destabilising their Catalan visitors.

Hansi Flick, Barcelona's coach, a figure replete with experience of confronting, and indeed vanquishing, Dortmund from his tenure in the Bundesliga, articulated his anticipation of an arduous second leg, notwithstanding his team's four-goal advantage, attributing this foresight to the fervour of the home crowd.

"I harboured a nascent intuition that such an eventuality was on the horizon," Flick confided to the broadcaster Amazon Prime. "On this occasion, one must extend congratulations to Dortmund, for their exceptionally executed match, and equally to my squad, who have secured their passage to the semi-finals."

The usually formidable attacking duo of Raphinha and Robert Lewandowski, boasting a combined 23 Champions League goals this term, endured an uncharacteristically subdued outing for Barcelona, with Raphinha's languid effort at Gregor Kobel's goal representing their most substantive scoring opportunity.

Guirassy, whom coach Niko Kovac hailed as Dortmund's "life insurance" following a match that further underscored his burgeoning ascendancy and cemented his status as the current Champions League top scorer, "merely necessitates the backing of his fellow players, an exigency inherent to any centre-forward, which he duly received today."

Dortmund had arguably forfeited the quarterfinal in the initial leg, further compounded by the eleventh-hour withdrawal of captain Emre Can and midfielder Carney Chukwuemeka due to debilitating injuries sustained earlier that day.

For a fleeting moment, Guirassy rendered the unattainable a tangible prospect.

Guirassy, having failed to capitalise on opportunities in the initial fixture and squandered a further pair early in Tuesday's encounter, demonstrated unerring precision from the penalty spot in the eleventh minute following a collision between Barcelona custodian Wojciech Szczesny and Pascal Gross.

Guirassy's aerial prowess extended the lead to two goals to nil in the forty-ninth minute, a situation compounded for Dortmund by Ramy Bensebaini's unfortunate own goal, catalyzed by Fermín López's incisive low delivery deflecting off Bensebaini's ankle – a double setback, given the defender's instrumental role in Dortmund's nascent recovery effort, having provided the assist for Guirassy's preceding goal moments prior.

Guirassy capitalized on Ronald Araujo's defensive misjudgement to seal his treble with a blistering near-post drive in the 76th minute, thereby assuming the mantle of the Champions League's pre-eminent marksman this campaign with a tally of 13 goals.

This turn of events injected Dortmund with renewed optimism concerning the potential orchestration of a truly legendary Champions League resurgence – a comeback that would arguably stand shoulder-to-shoulder with Barcelona's celebrated vanquishing of Paris Saint-Germain in 2017 – though ultimately Barcelona maintained their advantage to secure progression.

Advancing to the semi-finals, a stage not attained since the 2018-19 campaign, Barcelona is poised for a challenging encounter against either Inter Milan or Bayern Munich; concurrently, Paris Saint-Germain secured their place in the last four, notwithstanding a 3-2 defeat in the second leg, by prevailing over Aston Villa with a 5-4 aggregate scoreline in Tuesday's parallel fixture.

The setback constituted Barcelona's inaugural defeat across all competitive fronts since the 2-1 reverse against Atletico Madrid on December 21st, their first Champions League loss since September, and merely the seventh in Flick's fifty managerial outings, a record preceded by the German tactician's unblemished seven-game winning streak against Dortmund at the helm of both Barcelona and Bayern.

The hallowed turf of Dortmund's stadium may remain silent to the stirring strains of the Champions League anthem for a considerable period yet.

The preceding season's Champions League finalist is currently positioned eighth in the Bundesliga, residing six points adrift of the quartet of Champions League qualification berths with only five fixtures yet to be contested.