Al Kazeem produced a tremendous performance to lower the colours of hot favourite Camelot in the Tattersalls Gold Cup at the Curragh.
Roger Charlton's British raider was settled in last place of the four runners, just behind Camelot, as the market leader's stablemate Windsor Palace took them along in single file.
All looked to be going well enough for Camelot but James Doyle ranged upsides at the quarter-mile pole on the lightly-raced Al Kazeem (9-4) and it soon became apparent he had his measure.
Quickening in great style, Charlton's five-year-old claimed the Group One prize with something in hand.
"We can look at all the top races over a mile and a quarter and we also know he stays a mile and a half very well" - Roger Charlton on Al Kazeem
A length and a half was the winning margin for Al Kazeem, who was having just his second start since victory in the Jockey Club Stakes at Newmarket last May.
Doyle said: "He was so impressive at Newmarket and I was really excited, so to find out he had got injured during that race, it was hard to take.
"But Roger said we would get him back and it's great to see it all come together. He's got lots of class and hopefully we will have more fun with him."
Al Kazeem had returned this season at Sandown in April, winning the Gordon Richards Stakes by a length from Thomas Chippendale.
Doyle said: "We still left a lot to work with at Sandown, we wanted to use that as a stepping stone and he was able to win without having a hard race.
"He came on leaps and bounds and showed that today.
"He has lots of class, you have to respect Camelot and all he has done - at the two pole I couldn't believe how well I was going."
Charlton said: "He's been a slow maturing horse. Last year he came home with a stress fracture of his pelvis in the Jockey Club Stakes.
"His work has been really impressive and James said the ground was bit lively for him there.
"He's a good horse and he rode him confidently. The plan was to drop in behind Camelot and he rode a good race.
"We can look at all the top races over a mile and a quarter and we also know he stays a mile and a half very well.
"I'd like to think maybe the Arc at the end of the season. Ascot is an obvious possibility, we've also got the Eclipse - there's lots of lovely races there for him."
Doyle was riding his first winner in Ireland and was recording his second Group One winner after the Charlton-trained Cityscape in Dubai last year.
He added: "All credit to Mr Charlton - he's done a fantastic job with the horse and he's done a fantastic job with me as well. He took me on - I'd never even ridden in a Group One race before and he gave me a massive opportunity in Dubai and it paid off.
"Without people like him I'd probably be doing OK but I wouldn't be here today in these type of races.
"He's a great boss and a great person to work for. He gives me great confidence.
"My grand-father is from Monasterevin. He's 75 now and he'll be at home watching. My mother used to train and right from an early age I had ponies and stuff. I started riding out when I was about 12 years of age. It went from there.
"I'm 5ft 10. It's not easy but as I've got older I've become more disciplined. I can comfortably do 8st 10 so it's grand."
Despite being out of luck in the Tattersalls Gold Cup and in the Irish 1,000 Guineas, Aidan O'Brien and his jockey son Joseph still managed a double with Sir John Hawkins and Leading Light.
Big things are expected from Leading Light (4-6) after he swept to a cosy two and a quarter length victory from Little White Cloud in the Airlie Stud Gallinule Stakes.
Given a positive ride from the front, it looked like the Montjeu colt might be swamped by Little White Cloud at the two-furlong pole but he found plenty when asked.
O'Brien snr said: "He's lazy, that's why he wears the cheekpieces. It helps him from being too lazy early on.
"He's a possible for Ascot or the Irish Derby. He wouldn't mind 10 furlongs, a mile and a half or even two miles - I don't think it matters to him."
Sir John Hawkins is a possible for the Coventry Stakes at Royal Ascot after making a winning debut in the Big Bad Bob EBF Maiden by three-quarters of a length from Intensified.
"We are delighted with him. He was very green and learnt an awful lot there," said the trainer.
"His father (Henrythenavigator) and mother (Peeping Fawn) won four Group Ones each, so he is very well bred.
"I was afraid he might be a bit babyish, but he got a lovely lead and loves the fast ground."
Trainer Michael Halford and jockey Shane Foley got in on the double act through Paddy The Celeb (12-1) in the Irish Daily Mail Handicap and Via Ballycroy in the Texacloth Handicap.
Trainer Jim Bolger took the concluding Newstalk 106-108 Maiden with Maggie Dalton (14-1), ridden by Kevin Manning.