Caspian Prince got the better of a thrilling battle with Marsha to spring a surprise in the Friarstown Stud Sapphire Stakes at the Curragh.
Having won last year's Prix de l'Abbaye and finished third in last month's King's Stand at Royal Ascot, the Mark Prescott-trained Marsha was all the rage for this Group Two contest as the 1-2 favourite.
Three-time Epsom Dash winner Caspian Prince, trained by Tony Coyle, was a 10-1 shot stepped up in grade and cut out much of the running under Declan McDonogh.
Luke Morris asked Marsha for her effort in the final furlong and she drew alongside to set up a grandstand finish.
Both horses fought tooth and nail to the line and flashed by almost as one, but the judge confirmed Caspian Prince the winner by a short head.
Winning owner Stephen Louch said: "It's always going to be close in a race like that. I didn't expect to come and beat Marsha today. She's a good horse and we knew we were in with a chance, but to actually achieve it and get a Group race under his belt is brilliant.
"He is a star and it's fantastic. We picked him up in the sale at Deauville. From that day forward we have just fallen in love with him and won't let him go.
"We want to see him finish his career hopefully with a few more nice wins."
Coyle was only narrowly denied a big-race double as his Snap Shots went down by just half a length to Tithonus in the Tote Scurry Handicap.
The Denis Hogan-trained Tithonus was 10-1 to follow up his Rockingham triumph of a fortnight ago and did so in good style under Gary Halpin.
Hogan said: "That was class. I was a little worried coming to the Rockingham that he'd need the run and I knew he'd only improve coming here. He did and hopefully he can again.
"We were thinking about the seven furlongs in Galway at the weekend. It's another good pot.
"I'd imagine he'll get an entry in the Ayr Gold Cup. He's 90 today and might end up in the Silver Cup."
Actress provided Aidan O'Brien with an 11th victory in the Jebel Ali Silver Jubilee Anglesey Stakes.
The daughter of Declaration Of War has had plenty of racing already and took on the boys on the back of defeats in the Albany Stakes at Royal Ascot and when odds-on in a Listed race at Tipperary.
She disputed the early running with Brother Bear and Theobald in the centre of the track and as 9-10 favourite Brother Bear hung left to the rail, Actress (7-1) stayed on a true line and came home a length and three-quarters to the good over Theobald.
Winning rider Seamie Heffernan said: "I rode her last week over five and I thought they didn't go quick enough for me as I thought she was an out-and-out sprinter. I didn't think she'd see out the (six-furlong) trip as well today, but I kept her at it."
Perhaps the most visually impressive winner of the day was the O'Brien-trained The Pentagon in the opening Club Godolphin Irish European Breeders Fund Maiden.
Ridden by the Ballydoyle handler's daughter, Ana, the 9-2 chance made most of the running and pulled eight and a half lengths clear at the line.
Severus justified 4-1 favouritism in the K Club Handicap.