The teenager is currently in fourth place out of the 10 acts in the bookies’ odds to win the show.
Ladbrokes has him down at 12/1 to win the show, while William Hill has him at 8/1.
Leading the pack is Welsh choir group Cor Glanaethwy with odds of 11/10, followed by singer Calum Scott and dog act Jules and Matisse.
Isaac started singing at a young age and his talent was discovered at his dad’s boatyard at WicorMarine Yacht Haven.
A customer heard him singing under his boat and told his father.
After successfully auditioning for Prebendal choir school in Chichester, Isaac has never looked back.
He was head chorister for services at Chichester Cathedral and was named BBC Radio 2’s young chorister of the year in 2012.
Isaac, who now attends Portsmouth Grammar School and lives in Portchester, has been staying in a hotel in London over the weekend as he psyches himself up for his big moment on stage.
His talent has been honed through years of practice – sometimes up to 30 hours a week.
He said: “There’s a lot of vocal warming up. I’m going to have to keep learning the song and not forget how it goes.
‘It’s really about keeping in the zone.”
Among his biggest cheerleaders will be his 94-year-old great-grandmother Brenda Lepora, who will be watching from Whiteoaks Resthome in Fareham.
She told family that her darling ‘had made us proud’ and laughed that all the rest home residents were ‘on the edge of their seats’ as they watched the semi-final.
Isaac’s dad Scott Waddington, 46, said: “She said if he wins, she wants a big white Bentley car.”
The singer has wowed the judges and public with his performances, including a fabulous piano-accompanied version of Bonnie Raitt’s I Can’t Make You Love Me in the semi-final.
His dad, mum Imogen, sister Martha, nine, and brother Jack, 12, will all be in the audience tonight to cheer on Isaac.
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