The daughter of Declaration Of War had shown a good level of ability in three previous starts, with a Doncaster success sandwiched between two creditable placed efforts at Yarmouth and Nottingham.
Stepped up to Listed class in Berkshire, the 10-1 shot was settled at the rear of the group that raced on the far side of the track and once unleashed by Robert Winston, she showed a smart change of gear in the rain-softened ground to draw a length and three-quarters clear at the line.
Johnny Murtagh's Irish challenger Sankari Royale was a clear second ahead of Mrs Gallagher in third.
Ivory did not attend the meeting due to a stomach bug, but said from home: "That was just the ticket. She's a nice filly that we've taken our time with and going into today, I thought she might come home well to finish third or fourth and maybe pick up some black type.
"I suppose it's the manner of her win that's surprised me more than anything. She wasn't that well drawn and yet she's won so convincingly.
"She's almost won a Listed race too early, if that makes any sense. I'm going to have to go back to the programme book and see what we can find for her."
Ryan Moore delivered John Gosden-trained newcomer Purser (2-1) with a beautifully-timed challenge in the opening division of the Don Deadman Memorial EBF Maiden Stakes, collaring 15-8 favourite Merlin Magic by a head.
Thady Gosden, son and pupil assistant of the winning trainer, said: "He had a fantastic ride under hands and heels from Ryan Moore. It was the perfect example of how to ride a two-year-old.
"I think seven furlongs will be his trip at the moment. It was a little bit too soft for him and he will probably like good or better ground."
After filling the runner-up spot on his Doncaster debut, Sir Michael Stoute's 11-8 favourite Qaroun went one better in the second division under Frankie Dettori.
Harry Herbert, racing manager for owners Al Shaqab Racing, said: "Frankie likes him and he is a work in progress. He will probably only have one more run this year.
"We will not go too ambitious and we will probably look for a conditions race or something like that. Frankie said you don't want to be going to the well too much this year.
"I think that ground was soft enough for him. I loved his attitude - he has got a very good attitude."
Dettori and Gosden then teamed up to complete trebles on the afternoon, with Great Sound landing the Berry Bros. & Rudd Cellar Plan Handicap and The Mums coming good in the Highclere Thoroughbred Racing EBF Fillies' Novice Stakes.
Great Sound was the 6-4 favourite for his assignment and carried the colours of the Bermuda Thoroughbred Racing Limited syndicate to a half-length victory, gifting part-owners Chris Clark and Pam Rutherford an early wedding present
Herbert also runs this syndicate, and added: "Frankie said that he is very relaxed and just does the bare minimum. He is very progressive and he stays really well.
"It is a perfect wedding present for Pam Rutherford and Chris Clark, who are both part of the syndicate and are due to get married next Saturday."
The Mums (11-4) got home by a nose in the six-furlong novice event.
Rowan Scott made his first trip to the track a winning one after steering Pat Shanahan's Set In Stone (9-1) to a facile success in the Christopher Smith Associates Handicap.
Scott said: "Newbury is a lovely track to ride at and I would love to have more winners here."
The jockey and trainer then doubled up with 5-1 shot Fivehundredmiles in the Mobile Pimm's Bars Apprentice Handicap.
Ron Harris celebrated his first winner at the track in more than 11 years after Under The Covers demonstrated the best of her battling abilities in the Big Group Insight Handicap under Sam Hitchcott.
Harris said of the 20-1 winner: "She is a big-topped filly and we thought the soft ground would help her. It has proved today that she loves that ground and a flat track.
"It is lovely to have a winner at Newbury. It is one of the top grade tracks and that's where you want to be."