Shining Emerald lowered the colours of odds-on favourite Guerre in the Listed Blenheim Stakes at the Curragh.
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The 7/2 second favourite ran out an emphatic winner, staying on strongly in the final furlong to deny Aidan O'Brien's colt by three lengths.
Lady Ultra and Freedom Square led the field over the first few furlongs as Shining Emerald and Guerre travelled sweetly behind the front two.
Joseph O'Brien asked his mount for an effort two furlongs from home and the response was immediate as his two-year-old hit the front.
However, although it took the winner longer to get into his stride, he finished his race off much better than the runner-up and galloped on resolutely to land his first Pattern race for local trainer Paul Deegan.
Deegan said: "I'm absolutely delighted with him. He quickened well and put it to bed well. He's smart.
"I was concerned about the ground, but it's nice he showed he can change gear and change gear very effectively on nice, good ground.
"He's exciting and he's not done with for the year yet. We might have to revise plans now. He could go to England."
Jockey Chris Hayes was also impressed with his mount following the race.
"He's done that nicely," said Hayes.
"He annihilated an ordinary field at Listowel but probably didn't get the credit he deserved."