Fascinating Rock was awarded the Derrinstown Stud Derby Trial at Leopardstown after first-past-the-post Ebanoran was demoted to second by the stewards at the Foxrock venue.
The John Oxx-trained Ebanoran had benefited from a tactically astute ride by Declan McDonogh to take top honours, but there was interference in the closing stages as he came off the rail, leading to a detailed deliberation by the officials.
Ballysax Stakes winner Fascinating Rock was the even-money favourite to complete a treble on the afternoon for Dermot Weld and Pat Smullen, with last year's Beresford Stakes winner Geoffrey Chaucer rated the main threat on his return to action.
Smullen settled Fascinating Rock at the back of the field in the early stages, but rank outsider Highly Toxic was setting a sedate gallop. McDonogh significantly committed for home rounding the home bend aboard 8-1 shot Ebanoran and it proved a crucial move.
The Oasis Dream colt showed taking acceleration to run to the lead in a matter of strides and Fascinating Rock remained at the back of the field. When the market leader did find top gear he made inroads quickly, but it was all too late as Ebanoran had enough in hand.
Geoffrey Chaucer ran with plenty of credit in third on his first appearance since the end of September, also suffering interference.
Speaking before the outcome of the inquiry was known, Oxx said: "He's a good horse with a good turn of foot and he's going the right way.
"He's by a sprinter (Oasis Dream) out of a stayer (Ebadiyla), but putting speed into his pedigree was what the family needed. There is no end of stamina on the dam's side and she's a half-sister to two Ascot Gold Cup winners."
Weld said: "I don't want to win any race that way (in the stewards' room). I thought he was the best horse on the day and interference happened, but it was a very messy race. Pat was adamant that the interference cost him the race.
"He's a big, long striding horse and as they quickened off the home turn, he just lost his hind-end momentum. Pat gave him a few seconds to recover, which was the right thing to do.
"I've been teaching him to settle and switch off at home and it's the first time he's really been asked to sprint. It just took him a few strides to react. I'd be pretty definite that he'll go to Epsom and he'll certainly have learned a lot today.
"His half-brother was second in the Leopardstown November Handicap last year, so you'd have to he hopeful that he'd get the mile and a half."
Fascinating Rock has been cut to 16/1 (from 20/1) by Sky Bet for the Investec Derby while Ebanoran has also been cut to 20/1 (from 33/1) for the same race.