Under OW rules, lounge access is based on departing flight, not just whether there is a flight that day from some airport
I know people who have been denied access to the Sydney First lounge when not departing in 1st from Sydney
from oneworld
Originally Posted by ow.com
If your oneworldŽ frequent flyer tier status is Emerald or Sapphire, or as a First or Business Class traveller on a oneworld member airline, you can access more than 550 airport lounges throughout the world.
This means you can relax or catch up with work in comfort and style before departure, regardless of which oneworld member airline you choose to fly.
To be eligible, you must be departing on a flight that is both marketed and operated by a oneworld member airline