Politeness has defied the prevailing racing pattern at Flemington on Derby day to post her first Group One win in the $500,000 Myer Classic.

While the majority of winners had made their runs along the inside rail, Politeness ($19) came down the outside to outgun Fenway ($26) by three-quarters of a length with Azkadellia ($11) flashing home late between horses to grab third.

Sydney mare Royal Descent started favourite but never raised the hopes of her backers and finished down the track.

Politeness gave Robert Smerdon his first Derby day winner and the trainer said the Myer Classic had been a long-term plan as they looked to get a Group One win on the mare's record to boost her worth as a broodmare.

"She'd won about five Group Three races and the only way her long-term value could increase was to win at Group One level," Smerdon said.

"So we made this race our target."

Smerdon admitted to pre-race concerns about the apparent track bias towards the fence but his idea to ride the mare for luck was overruled by owner Phil Sly who insisted she be given room to unleash her trademark finish.

Politeness did the rest for Dwayne Dunn who picked up the winning ride due to a suspension to regular jockey Mark Zahra.