Sovereign made most of the running to land the Dubai Duty Free Irish Derby at odds of 33/1 under Padraig Beggy at the Curragh on Saturday.
The son of Galileo was one of the least fancied of the Ballydoyle quintet after helping to force the pace in Derby trials at Leopardstown and in the Investec Derby at Epsom.
Set the role of pacemaker again at the Curragh, he set a strong gallop along with Norway but he didn't see another rival after shrugging off his stablemate in the home straight.
Epsom winner and 5/4 favourite Anthony Van Dyck emerged from the chasing pack to run into second, but he was six lengths adrift of the winner at the line.
Jockey Beggy was bagging a second Classic success after his Epsom win on 40/1 chance Wings Of Eagles in 2017. It was his first win from 10 rides this season.
Trainer Aidan O'Brien has won the Irish Derby more times than Beggy has had rides this season, Sovereign's win taking his tally to 13.
"They were all there and they were all trying their best," said O'Brien.
"It was all very straightforward. Everyone knew Padraig was going to lead and Seamus (Heffernan, on Norway) was going to follow him.
"The race maybe unfolded a little bit unusually. What happened was that Donnacha's (O'Brien, on Broome) horse missed the break, he came out very slow and everyone might have expected him to fill the third position.
"Then Kevin (Manning, on Guaranteed) decided to take up that position. The lads had a nice lead, but they were still close enough. Padraig set perfect fractions, increased it from halfway and he wasn't for stopping.
"It was going to be a solid race. It was going to be a full mile and half and this track lends itself to that.
"They have to get the trip. This place is very uncomplicated and there is nowhere to hide out there.
"This horse had a very good run last year when Donnacha rode him in the Beresford ahead of Japan.
"He won his maiden by 10 lengths in Galway before that and it was always there. He's a Galileo and when they start galloping they usually don't stop.
"I'm delighted for Padraig and everyone involved with him."
Sovereign's price was cut in half for the St Leger, with some bookies going 10/1 for the Doncaster Classic.
O'Brien added: "The winner is a staying horse and he's going to stay well. He won't mind going the Leger trip.
"He's a solid horse to have because he'll jump and he'll go along in any kind of good race.
"He could go to the King George or go to the Grand Prix de Paris in France and then could have a break and go to the Leger.
"He's a solid horse and very uncomplicated. Padraig gave him a great ride.
"Ryan's horse (Anthony Van Dyck) ran very well. He was the only horse to chase after him (Sovereign), but probably Padraig was gone at the time.
"I thought he ran very well. We were going to decide with him after this whether we go to the Grand Prix de Paris or the King George.
"I'd say they are still options as there was nothing wrong with the run.
"Broome never got going at all."
Beggy said: "I'm over the moon. This would be more important to me (than the Epsom Derby) as an Irishman, the Irish Derby.
"I served my time with Kevin Prendergast just up the road and this was the race that you grew up wanting to win. That was my main aim as an apprentice.
"I'm just very, very lucky that I've won the English Derby and the Irish Derby. That is down to a big group of people, but I would have to say mainly Aidan O'Brien to put me on. Aidan would give you confidence and that helps.
"I just got into a lovely, comfortable rhythm and I felt like I could go quicker all through the race. My horse really enjoyed it here, a big galloping track.
"I knew I was after quickening and lengthening up the straight. I did think that something would be coming to me, but when I was close enough to have a peep at the big screen I knew I was clear.
"I just said keep him organised to the line now, you've won. Dreams come true!"