Follow The Plan was the surprise winner of the Punchestown Gold Cup as favourite Kauto Star was pulled up.
Kauto Star, the 11-year-old two-time Cheltenham Gold Cup winner, looked a spent force for much of the race before Ruby Walsh decided enough was enough.
Roberto Goldback was leading until jockey Robbie Power was spectacularly unseated at the last fence.
Follow The Plan (20-1), ridden by Tom Doyle, won by 11 lengths with Vic Venturi second and Rare Bob third.
Kauto Star's trainer Paul Nicholls said he would not rush to a decision about the future of the two-time Gold Cup winner following his disappointing performance.
"I said to [partner] Georgie [Browne] before the race that I didn't care where he finished as long as he came back safe and sound and after he'd jumped three or four it was obvious where he would finish. He was not firing today," he said.
"I'd done things a bit differently with him this year and had him fine-tuned for Cheltenham and then might have been a bit easy with him before this.
"But I'm not going to make any rash decisions based on one run. You could have a six-year-old that runs badly at this time of year and then comes back.
"We were in unknown territory running him in May and he'll have a summer's grass now. It's hard to judge on one run, but if he came back in the autumn and ran once more like that then obviously we would retire him."
In a race full of surprises, the two horses expected to give Kauto Star most to deal with, Kempes and Nacarat, failed to rise to the challenge.
Outside the top three, Aintree winner Nacarat was the only horse to finish the race.
Rare Bob did most of the early pace-setting, while Kauto Star jumped comfortable in the early stages without looking the winner.
He was the first horse to be pulled out of the race, although Walsh did canter the 10-11 favourite past the post.
"Kauto never jumped better than he did today but he never travelled," added Walsh.
Tranquil Sea unseated Andrew McNamara four out once the race began in earnest, and his error set up Roberto Goldback.
But instead it was Follow The Plan, trained by Oliver McKiernan, who registered an emphatic victory as fatigue took its toll on the others.
"We came here more or less for place money, we thought," said a delighted McKiernan.
"There again we thought if Kauto Star didn't run his usual race then we might have a better chance. This was our local track so were happy to come here.
"We were hopeful going to the last as our horse finishes strong. My opinion was our horse was the freshest horse in the race coming here so we thought it might give him a good chance.
"He was suited by the fast gallop as he failed to settle early at Aintree on his latest run. We were hoping he wouldn't be out of his depth and he's finished for the season now."