It was a reaction similar to that received by singing sensation Susan Boyle when she first stepped on to the TV talent-spotting show's stage for her audition, announcing that she wanted to be "as successful as Elaine Paige".
And like the 49-year-old from Blackburn in West Lothian, Gilmerton's very own opera singer blew everyone in the audition room away with his rendition of Russell Watson's Nella Fantasia, quickly turning their laughter to cheers.
Antonio, 20, said: "The audience were laughing at me at first because I told them I was a karaoke singer, and then when I started singing they just kind of couldn't believe what I was doing.
"I think it was because of the whole surprise with my act, no-one was expecting me to do that. They got behind me a lot and I had a standing ovation throughout the whole song.
"Piers Morgan said it reminded him of Susan Boyle's audition. It was the best compliment I have ever had."
The former Liberton High School pupil added: "It was really nerve-wracking. I have never been so nervous in my life but it was worth it.
"Amanda Holden said I was a breath of fresh air and Simon Cowell said I had the potential to be a really good artist.
"I felt overwhelmed, I have never done anything like this before and it just felt amazing."
Antonio has been singing opera for around four years, making a living from performing in bars and clubs in the Edinburgh area.
He represented Britain in the World Karaoke Championships in Finland in 2008, taking second place.
Antonio, who was born in the same Welsh village as Tom Jones – Pontypridd, near Cardiff – auditioned for Britain's Got Talent in Glasgow in January and said he was one of around 100 acts to pass the audition stage, making it through to the "reveal round".
But he remained tight-lipped about whether he had progressed to the next round – the live shows.
His audition will be shown on the ITV1 show next month.
Antonio, who honed his singing skills on a karaoke machine, said: "I got into singing through listening to opera with my grandfather, Howard, and singing in the shower."
The opera singer's father, Ricardo, is originally from Barcelona. Antonio moved to Gilmerton with his mum Christine – who encouraged him to audition for Britain's Got Talent – five years ago.
Antonio, who said his dream was to represent Britain in singing competitions, added: "I would love to follow in Susan Boyle's footsteps. It would be awesome."