Another summer of change at Leverkusen saw Kasper Hjulmand replaced by Carles Martinez Novell after Die Werkself missed out on UEFA Champions League qualification by just three points, and the new boss cut a furious figure on the touchline here.
A strong start from the hosts saw Mark Flekken save from the lively Cole Campbell at his near post, but that proved only a temporary reprieve.
On eight minutes, Edmond Tapsoba was caught on the ball in his own box as he failed to clear a cross, and after being found by Francis Onyeka on the edge of the box, Lukas Petkov picked out the bottom corner to score his club’s first-ever top-flight goal.
Straight from the kick-off, the lethargic Leverkusen were caught cold with Tapsoba again the culprit.
His wayward square pass was pounced upon by Campbell, who drove to the edge of the box and doubled his side’s lead with a superb finish less than a minute later.
The home supporters could hardly believe their eyes, and there was blood in the water as the shell-shocked visitors continued to cough up possession.
After Malik Tillman had his pocket picked, Onyeka forced a smart stop from Flekken before Felix Keidel and Petkov saw rebounds blocked.
Leverkusen offered very little in response as Aleix García’s free-kick deflected against the crossbar, the closest they came in a miserable first-half showing.
And things got no better following the restart, as within 30 seconds of kick-off, Elversberg scored again.
Leverkusen’s dreadful defending haunted them again, with Petkov’s cross from the right met by David Mokwa, who got in front of his marker to glance into the far corner.
Die Werkself were at least able to establish a greater foothold on proceedings from there, but they still went into the final 15 minutes without having registered a shot on target.
Patrik Schick ended that wait when he diverted Ibrahim Maza’s wayward shot into the back of the net, reducing the arrears and set hearts racing among the home crowd.
Tension was heightened as stoppage time began, with Christian Kofane lashing home the rebound after Victor Boniface’s effort came back off the bar.
Leverkusen made comebacks look routine en route to the title two years ago, but weren’t able to complete the turnaround here as their club-record 20-game unbeaten run against promoted sides came to an end.
It’s a historic day for Elversberg, who become the first Bundesliga debutant since RB Leipzig in 2016 to avoid defeat in their first game.
Flashscore Man of the Match: Lukas Petkov (Elversberg)