Lightning Spear benefitted from a patient ride by jockey Oisin Murphy to win the Sussex Stakes at Goodwood.
The 9-1 chance finished third last year but this time, once Murphy found a small gap late on, he went through it to win by a length-and-a-half.
Expert Eye (4-1) was second for James Doyle with Lord Glitters (10-1) third.
It is a first British Group One victory for the in-form Murphy, who broke his duck at this level in Germany last weekend.
The David Simcock-trained winner had come close to Group One success on a number of occasions, including losing by a short head to Rhododendron in May's Lockinge Stakes at Newbury.
And Murphy admitted that the pressure was on him over the mile course on the second day of the Goodwood festival.
"I never ever get nervous before Group Ones, but I was nervous today and was trying to hide it down at the start," he said.
"He's deserved to win a major Group One. He loves travelling behind heels and I was sure Expert Eye was going to fade away at some stage.
"What a horse, what a training performance. At seven years of age, it's outstanding."
Much of the pre-race talk had been about the previously unbeaten Without Parole and although the son of Frankel was well placed early on in a slow-paced race, he faded out of contention to finish seventh.