Pathfork (2-1) made it three wins from as many starts in the boylesports.com Vincent O'Brien National Stakes.
But Jessica Harrington's two-year-old had to pull out all of the stops to see off Casamento, who only made his debut last week at Tipperary, in a thrilling renewal of the Group One contest.
The latter had made most before the strong-moving Pathfork threw down his challenge, and responded in kind as the two fought out a ding-dong battle at the business end.
Zoffany was sent off the 6-4 favourite but was one of the first of the principals to send out distress signals and was a never-dangerous third.
Harrington said: ‘Fran (Berry) said he had to be really tough and that he didn't really like the ground.
‘Pure class got him there in the end and it's just fantastic.
‘I felt sick beforehand and my panic during the race was that he was in front for so long.
‘I'm going to the sales at Keeneland in the morning and I'll make plans with the owners then.
‘He did have a very hard race there.’
Longhunter made the most of a drop in class to take the Irish Field Blenheim Stakes.
Not disgraced in either the Railway Stakes or the Futurity on his two previous starts, the Kevin Prendergast-trained youngster was sent off the 3-1 joint-favourite but had to scrap to take the Listed prize.
Declan McDonogh's mount had travelled sweetly throughout and all looked set fair when his fellow market leader Emperor Hadrian gave way at the head of affairs.
But Katla slightly got first run and it was only in the dying strides that Longhunter got up by a short head.
Prendergast said: ‘He is a good, genuine little horse. The ease in the ground was a help and he battled well.’
Good To Follow (100-30) was another for favourite-backers as he stayed on strongly for Pat Smullen to take the www.thetote.com Handicap, while 10-1 chance Admiral Barry took the Curragh Amateur Derby EBF Handicap with something to spare.
