Needing wins against Union and Heidenheim – the only two sides they had never beaten in their top-flight history – Koln fans knew survival was not on the cards ahead of kick-off.
It then took just 19 minutes for the home side to find themselves two goals down, first conceding a bullet header from Robin Knoche to mark his first Bundesliga goal of the season following a Christopher Trimmel corner kick.
The next corner also proved costly for the hosts as Faride Alidou unknowingly handled in the area, allowing Kevin Volland to dispatch from the spot.
There were few clear-cut chances for the remainder of the half, but on the stroke of half-time, yet another corner led to a goal.
This time, Rani Khedira hauled down Timo Hubers as the set piece was taken, presenting Florian Kainz with the opportunity to cut the deficit from the spot and setting up an intriguing second period.
The onus was firmly on the hosts to produce an unlikely turnaround after the break, and they could have been level had Alidou not mistimed his effort from close range.
A much-improved Koln performance led to an open second half, and after relying on the crossbar to keep out Robin Gosens’ header from a corner, the hosts drew level when Steffen Tigges’s close-range header left Frederik Ronnow with no chance.
Incredibly, they then found a timely winner in stoppage time after charging forward on the counterattack to net via Damion Downs, sending the home fans into raptures.
Timo Schultz’s side could yet make history, with no Bundesliga club having ever closed a gap to 16th as large as Koln’s with two games remaining. As for Union Berlin, safety is not yet assured, with just one point separating them from the relegation playoff spot.
Flashscore Man of the Match: Christopher Trimmel (Union Berlin)
