Hailing from a town with a population of around just 13,000 people, Elversberg earned promotion to the Bundesliga for the first time in the club's history last season.
While not much was expected of them, they surprised a lot of people - including Leverkusen - by bursting out of the blocks full of belief and purpose on Saturday.
Elversberg raced into a 2-0 lead inside the opening nine minutes through Lukas Petkov and Cole Campbell, then added a third via David Mokwa right after half-time.
Leverkusen fought back late with goals from Patrik Schick (77') and Christian Kofane (90+1'), but the newcomers held on for a famous win.
RB Leipzig 3-0 Borussia Monchengladbach
Leipzig dominated Monchengladbach at the Red Bull Arena and ran out as comfortable 3-0 winners after an imposing display in their opening match of the Bundesliga season.
Ridle Baku opened the scoring in the 25th minute, with Antonio Nusa adding a second early in the second half. Rocco Reitz completed the scoring against his former club with a strike in the 66th minute.
Borussia Dortmund 2-0 Hamburger SV
Dortmund controlled the game and rarely needed to get out of second gear despite going down to 10 men as they beat Hamburg 2-0 at Signal Iduna Park.
Serhou Guirassy opened the scoring inside the opening 10 minutes, with Giannis Konstantelias having shot deflected in off Sebastiaan Bornauw for an own goal just before half-time to put them in a commanding position.
Dortmund finished with 10 men after a late red card for substitute Samuele Inacio but still claimed a solid win.
Union Berlin 3-3 Eintracht Frankfurt
Union Berlin and Eintracht Frankfurt played a thriller at An der alten Forsterei, with the match ultimately ending up as a 3-3 draw.
Emmanuel Latte Lath put Union ahead in the third minute before Younes Ebnoutalib seemed to take the game away from the hosts with a superb hat-trick (10', 11', 67') to put Frankfurt 3-1 up.
However, Union Berlin showed a lot of heart to fight back through goals from Leopold Querfeld (79') and Tim Skarke (90+2') to rescue a point in a high-scoring draw.
FC Koln 3-2 TSG Hoffenheim
Koln overcame being behind twice at RheinEnergieStadion to get their Bundesliga campaign off to a winning start with a hard-fought win.
Hoffenheim led through an Adam Daghim goal in the 27th minute before Saïd El Mala equalised six minutes into the second half
Ozan Kabak restored the visitors' advantage in the 67th minute, but Koln turned things around in the latter part of the second half. New signing Thijs Dallinga scored a fantastic brace in the 72nd and 82nd minutes to secure a dramatic home victory.