Matthew Macklin was stunned in 10 rounds in front of a shell-shocked crowd in Dublin.
Jorge Sebastian Heiland proved a handful throughout, giving Macklin a rough night throughout before a pinpoint southpaw right hook sent Macklin down and out in round 10.
Afterwards, Macklin gave his opponent credit and said the finish came from fatigue more than the finishing shot.
John Joe Nevin improved to 3-0 with victory over Jack Heath.
Heath was down early from a body shot and dropped again moments later as an uppercut threatened to undo him. He was floored a third and final time from a right hand before the fight was stopped.