Willie Mullins fired seven darts at the Irish Cesarewitch but none had the answer to the late charge of the John Murphy-trained Brazos who caused a minor upset to score at 16-1.
Davids Charm, who took up a prominent position for much of the way, was one-and-three-quarter-lengths back in second, while Tony Martin's Mr Everest kept on admirably in third.
Shane Foley, who guided Brazos to victory, said: "Brazos relished the trip and the ground. He worked like a good horse the other morning and I am glad he showed it.
"He is not ungenuine – the blinkers are only on him because he idles. I had a lovely trip round. Sometimes there can be hassle in these big-field handicaps but everything was smooth here."
How the race was won
Sandymount Duke built up a useful lead during the middle part of the race but there was plenty of scrimmaging in behind as Like An Open Book unseated Julie Burke, badly hampering Ballydoyle's Cliffs Of Dooneen, who was pulled-up by Donnacha O'Brien.
Nessun Dorma fared best of the Mullins septet in fourth with the Closutton maestro also responsible for the well-backed 5-1 joint-favourite Exchange Rate who was fifth.
Foley felt that bookmakers had underestimated his mount and added: "When he won his maiden he beat Exchange Rate at Killarney.
"When I looked at the betting earlier I saw Exchange Rate was 5-1 and my horse was 33-1. I couldn't believe it."