Kauto Star was pulled up as Follow The Plan won a dramatic race for the Punchestown Guinness Gold Cup.
Roberto Goldback looked the likely winner and held a narrow lead when he unseated Robbie Power at the final fence. That left Follow The Plan (20-1) to come home clear of the Dessie Hughes-trained pair of Vic Venturi and Rare Bob.
Kauto Star was well behind when Ruby Walsh called it a day before the fourth-last, although he did canter him back past the post.
His trainer Paul Nicholls said: "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.
"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.
"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."
Winning trainer Oliver McKiernan said: "We came here more or else for place money, we thought. 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 we're 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."