The first recognised Derby trial of the Irish Flat season, the Ballysax Stakes has been a breeding ground of future Ballydoyle champions down the years, with O'Brien saddling six previous winners, including Galileo, High Chaparral, Yeats and Fame And Glory.
Battle Of Marengo won three of his four starts as a juvenile, and signed off with an impressive display in the Beresford Stakes at the Curragh. He is a best-priced 16-1 for the Investec Derby at Epsom on June 1.
O'Brien also has Eye Of The Storm, Foundry, Magician, Nevis and The United States engaged in the Group Three contest.
Another trainer with an outstanding record in the Ballysax is Jim Bolger, who has saddled seven previous winners of the race, including in the last three renewals.
The pick of three entries this year could well be Trading Leather, who won twice from four two-year-old appearances and was a fair fifth in the Racing Post Trophy at Doncaster. Bolger has also entered Alpinist, a winner on the opening day of the new season at the Curragh, and Beyond Thankful.
14 horses have been entered in the 10-furlong event, with Dibayani, High Octane, Imperial Concorde, Little White Cloud and Sugar Boy completing the field.
Sugar Boy won his last three races as a juvenile, and completed the hat-trick with a brilliant six-and-a-half-length win in the Listed Eyrefield Stakes at Leopardstown.
