O Ceallaigh © Photo Healy Racing
O Ceallaigh sprang a 33/1 shock in the opener a Fairyhouse as hotpot Stuccodor failed to peg back the front-runner in testing conditions.
Andrew Leigh made the running on the Peter Fahey-trained gelding, who had finished mid-division at Navan on his only previous start.
He was a few lengths clear with Sea Buckthorn before halfway and the pair extended their advantage turning for home in the two-miler.
They came back to the field after sloppy jumps two from home but while Sea Buckthorn had no extra O Ceallaigh kicked on again before the last.
Stuccodor was ridden into second at the final flight but the 4/11 favourite couldn't pick up on the run-in and went down by two-and-a-half lengths.
"His run in Navan was quite good but he was very keen that day," said Fahey afterwards.
"I said to Andrew going out that if nothing wanted to make it don't be afraid to go on. It's great for Andrew, who is a great worked in the yard and he isn't getting as many opportunities as he'd like at the moment.
"'m also delighted for owner Pat McCarthy, who is from Kilcock. I'm not sure we're we'll go next. We'll sit down, have a think, and make a plan."
It was a welcome winner for Leigh, his first since Blazing Sonnet scored at Thurles last January 30th.
He suffered an injury plagued time last year with a 3-month absence in the summer after fracturing his hand in a schooling fall.
(Additional reporting by Alan Magee)