World No 1 Andrew Selby suffered another Commonwealth Games nightmare as he was beaten by Motherwell 19-year-old Reece McFadden in a fiery flyweight first-round clash in Glasgow.
The double European champion from Barry was deducted two points in the last round for losing his gumshield as the irresistible McFadden did enough to seal by far the best win of his short career.
Selby, who also boasts two world championship medals in his collection, was also shocked in Delhi four years ago when he dropped a verdict to Amir Khan's brother Haroon.
"Everything went wrong in the third round," said Selby. "As soon as the bell went, it all went out of the window.
"I had my gumshield specially made and I've worn in at every tournament I've been in in the last four years and it's never come out.
"I'm in the best shape of my life and I don't know what went wrong. Maybe he just took me by surprise and he deserved the win."
Selby's defeat was another major blow for the Welsh boxing team following the decision by Games authorities to deny accreditation to his team-mate Fred Evans.
But it was a significant moment for McFadden, who rose to the occasion to out-hustle Selby in the opening round and maintain a tough momentum throughout.
Selby won the second to claw the scores back level and the messy last was rendered irrelevant by the points deductions, which effectively sealed McFadden's shock win.
Selby showed his frustration in the dying seconds by launching himself at McFadden, who celebrated at the final bell.
The Scot, who will next face England's Charlie Edwards, said: "I've fought some tough boys but he was the toughest I've fought in my life.
"The gold medal is mine. I've just proved it against the world number one and I'll beat Charlie Edwards next. Hopefully he'll keep his gumshield in."