Romain Brégerie opened the scoring early in the first-half as his header beat Jonas Lössl for the French defender's third goal in his last six domestic appearances.
A Marvin Matip own goal put die Nullfünfer back on level terms mid-way through the second-half, but only thirty seconds later Ingolstadt's Swiss full-back, Florent Hadergjonaj, gave die Schanzer all three points in a result that heaps a lot of pressure upon Mainz boss Martin Schmidt.
Die Schanzer dominant
Despite their lowly standing in the Bundesliga table and a return to the second division looking imminent, Ingolstadt's performances have been a lot better than their results may suggest.
The defeat at Borussia Dortmund before the international break was the perfect example, where with better finishing Maik Walpurgis' side may have returned to Bavaria with all three points.
Yet on Sunday afternoon, poor finishing was certainly not the problem as die Schanzer took an early lead courtesy of Brégerie. The French defender gave his marker the slip, from a Pascal Groß corner, and reversed a header beyond the outstretched palm of Lössl to send the watching Südtribüne into jubilation.
Incidentally, the former SV Darmstadt 98 and Dynamo Dresden defender, Brégerie, had gone a year-and-a-half without scoring a Bundesliga goal; before scoring three since mid-February, in the victory at Eintracht Frankfurt, the draw with 1. FC Köln and finally against Martin Schmidt's side on Matchday 26.
Since Yunus Malli's departure to VfL Wolfsburg in the January transfer window die Nullfünfer, Mainz, have dropped down the Bundesliga table and it was easy to see why in the historic Bavarian town. There had been no real game plan in the first-half, with the only real threat, Jhon Cordoba, hopelessly isolated against an Ingolstadt defence who were very happy to sit deep.
Such was the abject nature of the first half performance by the Rhineland-Palatinate side, the closest that they would come to an equaliser within the opening forty-five minutes was a long-range Levin Öztunali free-kick, which Martin Hansen - between the sticks for die Schanzer - elected to let run behind for a goal-kick.
Darío Lezcano had a golden opportunity shortly before the break to extend Ingolstadt's lead, although the Paraguayan's finishing deserted him as the 26-year-old hooked his effort into the side netting after Lössl had flapped at Markus Suttner's speculative long-range effort.
Mainz fight back
Schmidt, evidently displeased with his sides showing in the first-half, elected to make a half-time substitute as Gulio Donati replaced Leon Balogun and it nearly had an almost instantaneous impact. Brégerie's sliced clearance rebounded off Matip and straight into the path of Öztunali, who should have scored but instead forced Hansen into a smart save down low to his left.
Yet, the change certainly sparked die Nullfünfer into life and it was now the away side that were dominating the game. Their second-half pressure would eventually pay too, as Öztunali benefitted from one of the set-piece positions that Mainz were continually afforded due to the rash challenges of Matip and Roger.
The former Bayer Leverkusen man and a relation of Germany great, Uwe Seeler, whipped in a left wing free-kick that evaded everyone and squirmed past a hapless Martin Hansen. A further look showed that there was potentially a slight deflection from Matip, that could've made it even harder for the Danish 'keeper and so the Ingolstadt captain was awarded the unfortunate honour of an own goal.
Die Schanzer, Ingolstadt, wouldn't be pegged back for long however and only thirty-two seconds after Martin Schmidt's side levelled, Florent Hadergjonaj put the Bavarians back into the lead.
The Swiss full-back, signed from Young Boys of Bern in the summer, miss-hit his cross into the Mainz box, however the delivery looped its way up and over Lössl and into the far post to send the Audi Sportpark from misery to delirium in a matter of moments. His first for Ingolstadt and potentially a crucial goal in the Bundesliga relegation battle.
In what has been labeled a crucial week for both Ingolstadt and Mainz in their efforts to stave off relegation, it was the Bavarians who started the Englisch woche as they mean to carry on.
Although try as they might, Schmidt's side were unable to forge any real opportunities against a resolute Ingolstadt rearguard action, in what was an extremely edgy final fifteen minutes. Die Schanzer could have had more breathing space too, although Stefan Bell's last-ditch interception prevented Pascal Groß from making it three deep into added time.
Maik Walpurgis' side now go into what will be a crucial week in how their season pans out with real confidence, with two further relegation six-pointers ahead against arch-rivals FC Augsburg as well as SV Darmstadt 98.
Mainz however continue their descent towards the drop zone and with the tricky task of RB Leipzig and a trip to SC Freiburg ahead, the weeks end could see the Rhineland-Palatinate side occupy the relegation play-off spot.