Jim Bolger dominated the finish of the Tattersalls Irish 2,000 Guineas at the Curragh with Mac Swiney just edging out stable companion Poetic Flare.
Mac Swiney, a Group One winner at two, had disappointed on his return to action in the Derrinstown Stud Derby Trial, but was subsequently found to be suffering from a nasal discharge.
Poetic Flare was already running in his third Classic of the season, having won the 2000 Guineas at Newmarket before finishing only sixth in the French version just six days ago.
The race was run in a heavy rain shower as Rory Cleary, riding by far the biggest winner of his career, set out to make all on Mac Swiney and his rivals dropped away one by one.
Only stablemate Poetic Flare put up a challenge and Kevin Manning looked to be travelling marginally the better.
However, just when Manning began to ask his mount for everything, Poetic Flare hung across the track slightly, eventually being beaten a short head in the 100th running of the Classic. Van Gogh stayed on to be third.
Bookmakers responded by cutting Mac Swiney to a best price of 8-1 for the Cazoo Derby next month.
Bolger was not at the track, but his daughter Una Manning confirmed Epsom is the target for the winner.
She said: "I just spoke to the boss and obviously he's absolutely delighted with the horse and very pleased with Poetic Flare as well.
"I'd say it was probably a race for horses that stay the mile well with the conditions.
"The plan is to go to Epsom with Mac Swiney and we'll see how Poetic Flare comes out of the race before deciding whether he'll go to Ascot for the St James Palace."
Manning, who is married to the rider of the runner-up, hailed her father's decision to run both colts at the Curragh.
She added: "He's not afraid to take on a challenge. He was talking about running the two horses and I said 'wouldn't it be great if Poetic Flare won and Mac Swiney was second and then went to Epsom and did a New Approach'.
"It ended up the other way around. I myself am a little disappointed for Kevin that he wasn't on the winner, but on the other hand Rory has been such a loyal second jockey in the yard for so many years that he very much deserves this win.
"I think Kevin was happy enough to ride Poetic Flare. He said to me last week, after Longchamp, maybe we should just run the two of them in the Guineas and it would leave Mac Swiney right for Epsom.
"We've always had faith in Mac Swiney. He wasn't quite himself at Leopardstown, but that does happen with horses and nowadays we all know about the mucus because we can scope them, so it's different to years ago when you wouldn't know.
The winner is named after the Irish playwright, author and politician Terence MacSwiney and Manning added: "This is Rory's day and Mac Swiney's day and Terence MacSwiney's memory will live on for another while."
Cleary was thrilled to have landed an Irish Classic, but admitted he was struggling to register his achievement.
He said: "I still can't believe it. I was quietly nervous about having to ride him. I've never ridden a fancied horse in it - in a big race - never mind a Classic.
"He's such a special horse to get a ride on. The boss this morning just told me to jump out good and smart and ride a race on him and see how it unfolds.
"The further we went, the better he was going under me, and he stayed at it so well. I think the ground, with it being a bit on the wet side, his stamina really came into play.
"He's so honest - I just can't believe I'm after winning the Guineas. Kevin (Manning on Poetic Flare) came to me and we quickened away together again. I think they're two very smart horses.
"My lad really just stuck his head out for me. I think somebody was looking down on me because they made it easy for me."