Chicago Grey (25/1) landed the Red Mills Chase at Navan as market leaders Rubi Light and Hidden Cyclone disappointed.
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Rubi Light was sent off the odds-on favourite to complete a hat-trick in this Grade Two contest but Robbie Hennessy's stable star weakened quickly once his rivals joined issue on the turn for home.
Better had also been expected from Shark Hanlon's Hidden Cyclone but he, too, found little when push came to shove.
That left Foildubh and Chicago Grey to fight out the finish of the rearranged contest with Gordon Elliott's charge, the lowest rated runner in the field, scoring readily.
The 10 year old - who had finished a 16 length second to Rubi Light in last year's renewal - was gaining his first success since winning the National Hunt Chase at the Cheltenham Festival in 2011.
Elliott said of his two-and-a-half-length winner : "I thought he'd run well. He's had a wind-op and obviously the Grand National is the plan now.
"The ground was soft and it played into his hands. He'll go straight for the National now and I'd say the wind-op made a big difference to him."
Sky Bet cut the winner to 16/1 from 25s for the John Smith's Grand National at Aintree in April.