Wesley Ward's flying machine showed tremendous speed from the start and was soon in command under Frankie Dettori, who was winning the race for the third year running.
She had left a big impression with her victory in the Queen Mary Stakes at Royal Ascot over five furlongs and her class saw her through the extra furlong as the 2-7 favourite triumphed over the colts to claim Group One spoils.
The Freddy Head-trained Alrahma was second, with Aidan O'Brien's Peace Envoy third.
Al Johrah was fourth and Tis Marvellous, trained by Clive Cox, last of the five runners.
Lady Aurelia remained unchanged at 6-1 for the Commonwealth Cup at Royal Ascot with Paddy Power. Coral cut her to that price from 8-1.
"I was very excited and elated. It was wonderful," said Ward of his three-quarters-of-a-length winner.
"I trained her a little light to give her a bit of time after she came home (from Royal Ascot) and she came back a little tired after this race, understandably because she wasn't up to what she was at Ascot.
"She'd breezed four times up to this, so I think this race is going to set her right off to the next one and that's the Cheveley Park (at Newmarket)."
O'Brien was pleased with the way Peace Envoy finished the race.
Speaking from the Curragh, he said: "I'm very happy with him and I'd imagine he'll have no problem getting another furlong looking at that.
"He made up a lot of ground and came home very well."
Listed - East Cape Guineas
G3 - Kings Cup
G2 - Resource Recycling Superstars Championship
G3 - Lamb & Hayward 4&5yo Trotting Championship
G2 - Storer Motors Nz Trotting Oaks