Supasundae took charge of the Coral Cup for trainer Jessica Harrington and jockey Robbie Power at the Cheltenham Festival.
Owned by Alan and Ann Potts, the 16-1 chance came into his own approaching the final flight and was much too good for Taquin Du Seuil, who went down by two lengths.
Who Dares Wins and Monksland finished third and fourth respectively.
Power said: "He's galloped all the way to the line.
"He was a very, very good bumper horse and beat Yanworth in the (Ascot) bumper.
Harrington said: "I only inherited him this year from Henry de Bromhead so it's absolutely fantastic.
"Good ground was the real making of him. We knew he'd improve a real lot on that ground."
Power added: "The main priority going out was to get a good position and to find a bit of room.
"I had a lovely run the whole way. I was confident when we got better ground that he'd be a better horse.
"I said he'd be competitive in this race and thankfully he was."
Tombstone, the 7-2 favourite, was most disappointing.