Still basking in the glory of their narrow triumph over Bayern Munich in the previous round, Leverkusen’s Nordkurve set the night ablaze - both in spirit and spectacle - as flares engulfed the BayArena in a smoky haze, forcing an early pause in proceedings.
Yet, it was Koln who settled first, with their quarter-final run marking their deepest cup venture since exiting at this stage in 2010. Coincidentally, the last time they advanced beyond this stage, it was Leverkusen who ended their journey after extra time in 2001/02.
Alejandro Grimaldo twice came agonisingly close to breaking the deadlock, first rattling the crossbar with a stunning free-kick before narrowly missing the right post from close range.
As half-time approached, Leverkusen turned up the heat, but it was Gerhard Struber’s men who made headway in the final minute of stoppage time.
Capitalising on a defensive mishap, Damion Downs struck first blood with an unstoppable strike from a tight angle, stunning the home faithful against the run of play.
Die Werkself nearly struck back following the restart, as Florian Wirtz sent his rebound painfully wide of the left post after Jeremie Frimpong had drawn a sharp one-handed save from Marvin Schwabe.
Yet, their wastefulness proved costly once more, with Linton Maina embarking on a brilliant solo run before drilling a low strike past Matej Kovar into the far corner.
The hosts, however, halved Koln’s lead soon after on the hour mark, thanks to Patrik Schick’s unmatched composure inside the box as he buried a low shot from a tight angle into the right corner after picking up Wirtz’s slick pass.
Xabi Alonso then introduced centre-forward Victor Boniface in a bid to level proceedings, pairing him with Schick in a rare 4-4-2 setup. The move paid off in dramatic fashion, as Schick completed his brace deep into stoppage time, expertly nodding Frimpong’s cross into the far corner.
Riding the wave of momentum, Boniface repaid Alonso’s faith early in extra time, turning the match on its head with a poacher’s finish after latching onto Grimaldo’s lofted pass.
That didn’t dishearten the visitors in the least, with Imad Rondic soon burying Steffen Tigges’ pass from close range.
However, VAR had other ideas, disallowing the strike as Boniface’s extra-time winner ultimately helped Leverkusen avoid collapse in front of their home faithful.
Yet another masterful comeback means hopes of securing successive DFB Pokal titles for the first time ever remain strong.
Although the 2. Bundesliga leaders appear well-placed to make an immediate return to the German top-flight, Struber will rue his side’s defensive frailties as dreams of a rare season double go up in smoke.
Flashscore Man of the Match: Patrik Schick (Bayer Leverkusen)