Fancy Blue made her racecourse debut in a maiden race over seven furlongs at Naas Racecourse on 18 September and went off at odds of 6/1 in a fifteen-runner field. Ridden by her trainer's son Donnacha O'Brien she raced in mid-division before staying on strongly to overtake the favourite Chasing The Dawn in the closing stages and win by half a length. On 13 October the filly was moved up in class and distance for the Listed Staffordstown Stud Stakes over one mile on soft ground at the Curragh and started the 4/1 third choice in the betting behind A New Dawn and Auxilia. With Seamie Heffernan in the saddle she started slowly but produced a sustained run from the rear of the field in the last quarter mile to win by a head from A New Dawn after taking the lead in the final strides. After the race Aidan O'Brien admitted that Donnacha O'Brien had been handling the filly at Longfield stable, near Goold's Cross, County Tipperary and added "She’s a quality filly and Seamus gave her a lovely ride". When Donnacha O'Brien retired from riding at the age of 21 in November 2019, Fancy Blue was one of the horses to join his training stable at Longfield.
2020: three-year-old season
The flat racing season in Ireland was disrupted by the COVID-19 Pandemic and the Group 1 Irish 1000 Guineas was run three weeks later than usual on 13 Junebehind closed doors at the Curragh. Ridden by Declan McDonogh she started at odds of 12/1 in an eleven-runner field and stayed on well from the rear of the field, two lengths behind the winner Peaceful. On 5 July the filly was sent to France to contest the Prix de Diane over 2000 metres at Chantilly Racecourse in which she was ridden by Pierre-Charles Boudot and went off the 8.1/1 fourth choice in the betting behind Alpine Star, Peaceful and the undefeated Raabihah. The other seven runners included Speak of the Devil, Solsticia, Miss Extra, Ebaiyra and Magic Attitude. Boudot settled his filly in second place behind Alpine Star before moving up to take the lead 200 metres out. In a closely-contested finish Fancy Blue stayed on well under pressure to win by a short neck, a head and a head from Alpine Star, Peaceful and Raabihah. Donnacha O'Brien, who watched the event from Fairyhouse said "I always knew she was a very good filly and we always thought the step up in trip would suit her. It definitely did. Pierre-Charles is a very good rider and I told him beforehand he should do what he wants. There was no pace early so he went forward on her and sat upsides the leader. It was exactly what I would have liked him to do. She quickened up well and stuck at it. The home straight felt like a lifetime".