It was an 84th individual top-level winner for sire Galileo, equalling the record set by his former stud mate Danehill, and O'Brien's travelling head lad TJ Comerford felt better ground was crucial to her chances.
One of the most popular horses in Australia bowed out in typically honest fashion in the same race with Godolphin flagbearer Hartnell finishing a gallant third.
It was the 8yo 34th start in top-level company and 58th run. He is set to take in show classes in his post-racing career and will be looked after by his groom, Reg Fleming.
Hartnell started his career with Mark Johnston, for whom he won the Queen's Vase at Royal Ascot five years ago, before contesting many high-profile races for John O'Shea then Cummings for the last three seasons.