Carrickboy made just about every yard to land the Byrne Group Plate at the Cheltenham Festival.
Venetia Williams' charge finished sixth in the race last year but was allowed to go off at odds of 50-1 in the hands of Liam Treadwell.
He rode an excellent race from the front but trainer David Pipe appeared to hold the upper hand as his pair of Matuhi and favourite Ballynagour were lining up in behind to challenge.
However, Treadwell had conserved a little energy and pushed on again with only Vino Griego pursuing him.
The runner-up tried his best but Carrickboy proved too strong, winning by a length and a half from Vino Griego with Tartak third and top weight Hunt Ball staying on for fourth.
There was drama before the off, too, as leading fancy Cantlow was withdrawn at the start after bleeding from the nose while Mad Moose refused to jump off.
Treadwell said: "I've come close before but to finally win here is amazing.
"What a buzz I got out there, he jumped from fence to fence and I've been able to get a blow into him and he was game up the hill for me.
"His jumping was key today because I didn't want to press on too soon.
"It's great for Venetia and the team, they've had such a good year and a winner here as well is great."
Williams said: "It's extraordinary. I said to Liam to try to make all if you can, but how many horses make all in these Cheltenham handicaps?
"The thing is, if he'd been behind a wall of horses, he'd have curled up.
"The Irish and Nicky (Henderson) have won practically everything so to come through and win one is amazing."
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