Sky Lantern finished strongly to claim the Qipco 1000 Guineas at Newmarket.
Trained by Richard Hannon and ridden by Richard Hughes, the grey filly was a 9-1 shot to claim Classic glory having been beaten by the reopposing Hot Snap in the Nell Gwyn Stakes on her seasonal return.
The unbeaten Just The Judge looked likely to win when quickening up to lead heading inside the final furlong, but she was collared in the closing stages by Sky Lantern, who struck by half a length.
Champion jockey Hughes, who was claiming his first British Classic triumph, said: "They didn't go over fast - it was all about giving her plenty of cover.
"She was tough to see it out to the line."
Sky Lantern showed top-class form in her juvenile year, during which she won the Group 1 Moyglare Stud Stakes at the Curragh.
She appeared well held by Hot Snap on their recent course meeting but while that filly disappointed, Hannon's inmate rose to the challenge admirably to give an emotional Hughes a keynote success.
The victory comes 24 hours after Hannon's Toronado disappointed in the 2000 Guineas under Hughes.
Hughes said: "My wife was so upset (after Toronado's defeat) - I was consoling her all night - but today was great.
"I believed in this filly. I knew I gave her a bad ride the last day, but she's a good filly and loves that fast ground. It's thoroughly deserved.
"It's taken a long time (to win a British Classic)."
Richard Hannon jnr, the Herridge handler's son and assistant, said: "We were pretty low after yesterday.
"It was a very disappointing, but she deserved a bit of luck, this filly.
"She went to America (Breeders' Cup) and didn't get any luck and then she bumped into a very good filly (Hot Snap) who didn't run her race today.
"I'm delighted for Hughesie. He's one of the best jockeys ever and I'm just delighted he's done it on one of ours."
Just The Judge ran a superb race to fill the runner-up spot for trainer Charlie Hills and jockey Jamie Spencer.
Curragh maiden winner Moth, supplemented at a cost of £30,000, looked green coming out of the dip but finished off well to pick up minor honours for Joseph and Aidan O'Brien.
Just The Judge's owner Sheikh Fahad said: "She ran a fabulous race.
"She came there to win, she got to the front and looked like the winner from a long way out, but Hughesie has also ridden a great race.
"Sky Lantern has had a run (this season) and we haven't. She hasn't come in her coat yet, so I'm still pretty confident we can change it around later in the season."
Moth's rider, Joseph O'Brien, said: "She ran a blinder.
"I had to weave through to get a run and she stayed on well, but I think she'd be more suited by an even track as she's still quite green."