Following on from a hard-fought all-the-way French Oaks victory, the John and Thady Gosden-trained filly showed a completely different style of running on this occasion.
Dropped out last in the very early stages behind a slow pace, Doyle gradually moved closer to the main body of runners.
However, that meant Nashwa had to make up the ground in the hottest part of the race when all her rivals were quickening, too - but she was well up to the task.
As Dreamloper faded Fonteyn and Aristia were the main challengers, but Nashwa had too many guns and the 6-5 favourite beat Aristia by a length and three-quarters. Doyle's husband, Tom Marquand, finished third on Lilac Road.
"It's pretty awesome. She gave me some feel then," said Doyle, who was becoming the first woman to ride the winner of the Goodwood feature.
"We were drawn badly today, I rode her aggressively in France as we had a good draw so I wanted to hold my position. Today, in between her work from her previous run she knows what she is doing her, so I didn't want to light her up and ride her from a pace angle, so Mr Gosden told me to ride her that way today.
"I came down the hill with a double handful and she travels very well, but she takes a while to hit top gear. I was conscious about keeping her balanced down the hill.
"This is her perfect trip (10 furlongs). She has a high cruising speed and sees it out very well. She is push button and you can ride her anywhere which is really nice."
She added: "It's unreal, Nashwa is a horse of a lifetime and if it wasn't for Imad Al Sagar (owner) giving me this opportunity, I might not have enjoyed days like this."
Gosden senior said: "We were drawn nine and we didn't want to get caught on the outside with daylight.
"We've relaxed at the back in last and what they've done is suddenly pull the pace up and if you look at the fractions, they did two 14-second furlongs in the middle which is as slow as you can go. Coming from last made it tough on her as they are quickening down the hill and she has to get there, but Nashwa has got the class and when the ground levelled off she was happier and she won with a bit in hand.
"I think next time we might have to put a pacemaker in. She is versatile to do that from off the pace. She is a talented filly and I think we will stay in against the fillies in something like the Prix de l'Opera. I don't want to rush taking on colts this year, maybe next year.
"She's won with a bit in hand, but she is a grand filly who is improving all the time. Her owner-breeder Imad Al Sagar keeps pictures of her and she has changed a lot this year alone. I'll stay with the fillies at this stage in the Prix de l'Opera, but a bit more pace would have suited.
"We tried over a mile and a half at Epsom and she didn't quite get the trip. She's won the Diane and the Nassau so you can never ask for more from a filly. She has got the frame to improve again in the autumn and next year."
He added: "Hollie Doyle is a star. She has an incredible work ethic. As a rider, she is very savvy and strong with great balance. She has the most wonderful personality and she is so applied and focused - she is a credit to anybody in any line of work."