Inothewayurthinkin galloped on strongly up the hill to deny Galopin Des Champs a famous Boodles Cheltenham Gold Cup hat-trick.
Gavin Cromwell's seven-year-old was supplemented for the race at a cost of £25,000 and that proved another shrewd investment by owner JP McManus as he stormed home to score by six lengths at 15-2.
Galopin Des Champs, who broke the heart of Bravemansgame two years ago and was too strong for Gerri Colombe last year, was settled in mid-division as Ahoy Senor set the pace, but the defending champion was not quite at his fluent best over the early fences.
The 8-13 favourite survived a scare when slightly hampered by the fall of Ahoy Senor and seemed to be warming to the task as he swept into the lead turning for home.
However, Mark Walsh was stalking him on Inothewayurthinkin and his mount produced an impressive turn of foot to power clear.
"I'm absolutely speechless," said Cromwell to Racing TV.
"We’ve had a lot of faith in this horse. Credit has to go to Keith Donoghue with this horse, he’s been a part of him all the way.
"He’s done all the schooling and ridden him all the way along. I’m just thrilled.
"I was worried about the pace of the race on the better ground, he was only just hanging in there the whole time – he was flat out.
"He’s a very good horse. Going down to the second last I thought we had a good chance, what can you say? It’s brilliant, I’m just thrilled.
"Great thanks to JP and Noreen (McManus) for having the confidence to supplement him. It’s brilliant, they’re so good to train for. They’re brilliant people."
McManus said: "You have to enjoy these moments, they are so long in the making. We've had him since he was a foal, he was bred by (wife) Noreen. It’s a very exciting time and I will treasure it.
"I would like to see it again, I don’t think I took it all in, but it’s an exciting day."
But there was a sad note for the McManus team, with the Emmet Mullins-trained Corbetts Cross suffering a fatal injury in his fall at the second-last.
A statement from the British Horseracing Authority read: "In our fifth race of the day, Corbetts Cross was immediately attended to by our veterinary professionals, but sadly sustained a fatal injury. Our heartfelt condolences are with his connections."
