Benefficient produced a gutsy performance to land the Jewson Novices' Chase, the opening event on the third day of the Cheltenham Festival.
Tony Martin's charge was allowed to go off a 20-1 shot in the hands of Bryan Cooper but he made a mockery of his odds as he accounted for hot favourite Dynaste.
Benefficient had been prominent throughout but while he was headed some way from home, he found a second wind to power up the hill and win by three and a quarter lengths.
Cooper was positive from the off on his mount, disputing the early pace with Molotof before Dynaste started to make progress six fences from home.
Benefficient's challenge looked to be over as Dynaste assumed control at the top of the hill, with Captain Conan trying to go along with him while Marito made stealthy progress in behind.
However, Marito met the penultimate fence all wrong and crashed out while Cooper kept his composure, switching back to challenge up the inside, edging in front at the final fence before staying on powerfully.
Captain Conan faded up the hill, with 100-1 shot Changing Times finishing fast for third place.
Cooper said: "It's unbelievable, it's what you dream of as a young boy.
"Tony said to me that if he gets headed turning in, to just sit on him and let him fiddle away.
"Some of the others might have had more speed than him but they couldn't get away from me.
"He winged the last and galloped all the way to the line."