Coolmore finished with a rattle to claim top honours in the CL & MF Weld Park Stakes at the Curragh.
Aidan O'Brien's filly had let down odds-on backers on her first two starts, most recently by a head to the reopposing Anamba at Leopardstown.
Kind Of Magic played the role of pacemaker for the O'Brien team in this Group Three contest before folding, after which Last Waltz came through to lead.
Anamba loomed up to challenge inside the final furlong, but just as she was wearing down Last Waltz, 5-2 chance Coolmore and Joseph O'Brien picked up to beat them both.
Anamba ran a fine race on just her second start to fill the runner-up spot, beaten half a length.
The winner's stable companion How High The Moon was the 15-8 favourite, but she proved disappointing, finishing well down the field.
A full-sister to Gleneagles, Coolmore was cut to 16-1 from 25-1 with RaceBets for the Qipco 1000 Guineas and also the Investec Oaks
O'Brien said: "I'm delighted with that. I thought she would win in Leopardstown, but it was on the inside track and she was a bit green and the ground was a bit dead.
"I always thought she wanted to go a mile and she ran today to get more experience.
"She is crying out to go a mile this year. They went a good gallop and she came home well.
"I was disappointed with How High The Moon. The last day I thought a mile was stretching her a bit.
"She is still a bit babyish and is a big filly that will make a nice horse next year."
Earlier, Ryan Moore rode his first winner for O'Brien since returning from injury as Hit It A Bomb made a winning debut in the Irish Stallion Farms European Breeders Fund Maiden at the Curragh.
Moore had been sidelined by a neck problem sustained in a stalls incident at Newmarket in early July, but was back in the saddle and back among the winners at Newmarket earlier this week.
Hit It A Bomb was the 2-1 favourite for his racecourse introduction and was given time to find his feet by Moore.
Under pressure some way from home, he responded to his jockey's urgings to battle his way to the front and just had enough in the tank to hold 50-1 shot Agent Of Chaos by a neck.
Theodorico was placed for the third time in third.
O'Brien said: "He's a nice horse and ran green. He was drawn badly and did well to win. Ryan was happy with him.
"The Racing Post Trophy may come a bit quick, but we'll see how he comes out of this first. If he'd had a run (earlier) he could have been a Dewhurst horse.
"He handled that ground, but he's a War Front and would like some nice ground."
Jenniechild emerged victorious after a thrilling climax to the Irish Stallion Farms European Breeders Fund Maiden at the Curragh.
Down the field on her racecourse debut at Cork in June, Peter Fahey's filly fared much better when third at Down Royal little over a fortnight ago and was a 6-1 shot to make it third time lucky.
Colin Keane settled his mount in the middle of the pack in early stages of the five-furlong contest before angling wide to mount his challenge.
Piazzini ran her best race to date, sticking to her task well against the rail, but Jenniechild got up to beat her by a head.
Diamond Avalanche was third.
Fahey said: "She was very green on her debut, but had a lovely run the second day. More than likely that will be it for the season.
"It's great for Lucy (Lynch, owner) who bred her and also raced the dam."
