Oisin Fagan failed to take the biggest opportunity of his career as Amir Khan knocked him out in second round of their fight at the ExCeL Arena in London on Saturday night.
Fagan required oxygen treatment in his corner after a brutally one-sided contest was stopped by referee Mickey Vann one minute and 37 seconds into the round.
The victory, Khan's 19th in 20 fights, secured the Olympic silver medalist the vacant WBA international lightweight championship and was hugely impressive.
Khan, with his hands glued to his chin, used the ring to make himself an elusive target in the opening round as he found Fagan freely with his jab.
A strong right hand floored Fagan and the Irishman, operating on shaky legs, looked in serious trouble as Khan continued to land at will.
Fagan went down for a second time amid a flurry of punches and although he was saved by the bell, more punishment followed in an utterly one-sided second and the fight was over.
Khan's career suffered a significant setback with his first-round demolition by unknown Colombian puncher Breidis Prescott in September.
Flattened in just 54 seconds, it was the sixth time the 21-year-old had been knocked down and confirmed the worst fears over his vulnerable chin.
The defeat slammed the breaks on his world title aspirations and raised doubts over his ability to challenge for a major belt.
A bold next step saw Khan head to Los Angeles to seek the help of the highly-regarded trainer Freddie Roach to begin the rebuilding process.
Wary of the damage Prescott had inflicted, Khan's next opponent was picked with care.
Oklahoma-based Irishman Oisin Fagan had just 13 knockouts from his 22 victories and was not expected to provide too vigorous an examination of Khan's chin.
And so it proved as the 34-year-old was sent tumbling to the canvas twice before Mickey Vann had seen enough.