Coming into the game with their fate in their own hands on a dramatic last weekend of the campaign, the hosts started sluggishly at the Voith-Arena and fell behind after just seven minutes.
Kacper Potulski’s darting run into the penalty box was not tracked, and his cross was nodded home by Phillip Tietz from a yard out.
And Heidenheim struggled to react to that setback, as Tietz steered an effort against Frank Feller’s crossbar five minutes later.
The home side did rouse themselves to pose an intermittent threat before the break, as Eren Dinkci tested Daniel Batz from 20 yards and Marvin Pieringer was denied by the woodwork.
But the visitors doubled their advantage two minutes before the break, as Nadiem Amiri crisply finished off Tietz’s pass after a ruthless Mainz counterattack.
Despite the feeling that their destiny was already sealed at the start of the second period, Heidenheim showed real fight after the restart, with Jan Schoppner powering a header off the crossbar and Potulski being denied from close range, as a revival was briefly threatened.
However, that fizzled out after the hour mark, leaving the home fans to face the increasingly inevitable prospect of a return to the second tier for the first time since 2023. Batz remained alert to superbly claw away efforts from Patrick Mainka and Budu Zivzivadze late on, ultimately keeping the hosts at bay and ensuring Frank Schmidt’s team bowed out of the top flight in low-key fashion.
A 20th league loss of the season means Heidenheim end the campaign 17th in the standings, below VfL Wolfsburg, who battled to a 3-1 win at St Pauli to send the hosts down automatically, with Die Wolfe claiming the relegation play-off place in dramatic style.
As for Mainz, a 10th league win of the season sees them finish on a high in 10th place.
Flashscore Man of the Match: Daniel Batz (Mainz)