Ridden by Colm O'Donoghue, Black Bear Island (12-1) produced a fine finish in the final straight to pip stablemate Freemantle (13-2) in the Derby trial.
The Labour-run council planned to hold a local advisory referendum, asking people from the Freemantle and Millbrook wards if they supported the construction of the plant.
The bustling seaport of Freemantle lies 19km south-west of Perth where the Swan River meets the Indian Ocean and its historic heritage is clear for all to see.