Unbeaten in five previous starts, including an impressive victory in the Coronation Stakes on her seasonal bow at Royal Ascot, Inspiral was sent off the 1/7 favourite for the John and Thady Gosden team and jockey Frankie Dettori.
However, she was clearly in for a fight as Dettori got to work a couple of furlongs out, momentarily looking like getting the better of the pacesetting Prosperous Voyage but not finding that extra kick to pull clear of Ralph Beckett's 16/1 winner.
That allowed 1000 Guineas runner-up Prosperous Voyage a second bite of the cherry and jockey Rob Hornby galvanised her back into the lead, eventually coming home an authoritative length and three-quarters to the good.
Prosperous Voyage finished finished nine lengths behind Inspiral at Ascot, but Beckett felt the straight track at Newmarket had made a difference.
He said: "The key really to her is a straight track. Around a bend, she scraped home in a maiden at Epsom and got beat at Chester (last year), but when she's run on a straight track, she's run her race.
"Maybe Inspiral didn't turn up today, maybe she did bounce - there's lots of maybes, but this filly ran her race and that's all that really matters, if you're me anyway.
"The Sun Chariot is the obvious race for her. We will keep bringing her back to Newmarket."
It was consolation for Hornby after he missed the winning ride on the stable's Westover in the Irish Derby, with owners Juddmonte opting to give the mount to Irish champion Colin Keane at the Curragh.
Beckett added: "It was a good ride today. There's a certain amount of irony in that (owners) Andrew Rosen and Marc Chan are close friends of Frankie, but that's the way it goes - it's a horse race.
"I'm delighted for the filly as much as anything else and the rest of us are all just in her space.
"He gave her a lovely ride, he's done it before, he did it in France last year on Scope. It's not that we lack faith in our rider, it's just we have three jockeys - we don't have a stable jockey we have jockeys that ride work regularly - and if an owner wants a different jockey, then that's their prerogative."
Beckett admitted he had not gone to Newmarket expecting to beat Inspiral, but felt the race was the correct fit for his filly.
He explained: "I don't think we ran here thinking we would turn the favourite over, more that it was the right race for her.
"She didn't act in the Coronation Stakes because she's not as effective round a bend, we know that now.
"Sometimes it's not about whether you think you can win or not, it's what is right for the horse and today was.
"Rob has become an integral part of the operation. Whether he rides all the horses or not is not the be-all and end-all. He will ride what we think is right."
For his part, John Gosden felt Inspiral had "run flat" in the wake of her Ascot comeback.
He said: "You don't normally come here after a big win at Ascot, but she hadn't run all year.
"I think she's run a little flat. Yes the ground is quick enough, I'd agree with that, but I think it's more to do with a huge performance at Ascot. Having run only the once it made sense to come here.
"It can happen, when they run at Ascot and then come here, especially given she hadn't run since the previous October.
"We'll freshen her up and go again. She seems happy enough."