One Cool Cat lost on his debut start, finishing 4th in a maiden race at the Curragh. He was soon on the winning trail with a victory in a maiden race at York Racecourse six weeks later. The Anglesey Stakes was his next race, and was the second in a string of four consecutive wins, following up in the Phoenix Stakes and National Stakes. Aidan O'Brien had been so impressed with his work at home and also on the racetrack, that he joked once, "I think I'll move him in beside me and knock a door in the bedroom to put him up for the winter!"
For his performance in the 2003 racing season One Cool Cat earned the Cartier Racing Award as Two-Year-Old European Champion Colt.
A return to 6 furlongs was a victorious one, beating The Kiddykid by a length in the Group 3 Phoenix Sprint Stakes, again at the Curragh, at the start of August. Just eleven days later, he started as favourite for the Group 1 Nunthorpe Stakes at York Racecourse, finishing 3rd, although may well have won with a better run. The Group 1 Haydock Sprint Cup was next on the agenda 2 weeks later, but the 3rd run in such quick succession was seemingly too much for him, and finished 6th, 3 lengths behind the winner Tante Rose.