Carlingford Lough landed his fifth Grade One triumph as Cue Card came a tired fourth in the Gold Cup at the Punchestown Festival.
Cue Card, winner of the Betfred Bowl at Aintree, was an odds-on favourite but Barry Geraghty rode the John Kiely-trained Carlingford Lough to victory.
Djakadam was second, with stable companion Don Poli in third.
Carlingford Lough won the Irish Gold Cup at Leopardstown in February before finishing fourth at Cheltenham.
Kiely's charge, winner of the Galway Plate in 2013, was sent off 12-1 in a market dominated by much-loved British challenger Cue Card.
Road To Riches took the field along for much of the race and was tracked into the straight by Djakadam and Don Poli, second and third respectively in the Gold Cup at Cheltenham.
Cue Card, who suffered a dramatic fall at Cheltenham before winning convincingly at Aintree, did not travel with his usual panache, and had ground to make up turning for home.
The complexion of the race changed at the second-last, however, with Road To Riches coming to grief and both Djakadam and Don Poli beginning to falter.
Carlingford Lough made the most of the opportunity, joining Djakadam for the lead at the final fence before going on to triumph by four and a half lengths.
Cue Card ready for a rest
Joe Tizzard, son of and assistant to Cue Card's trainer Colin, put defeat down to it being "the end of a long season".
"He'll have a good rest now and will be back to fight again," he added.
"Whatever happened here, he's had a wonderful time, and we're very proud of him and what he's achieved."
Kiely, meanwhile, said not racing at Aintree had helped his charge.
"He likes this track and had a wonderful race," he said.