The fourth-placed Mariners were due to host Canberra at Industree Group Stadium on Sunday afternoon.
But the pitch was deemed unplayable, forcing the game's postponement until Monday evening - provided the playing surface is up to scratch by then.
"The Australian Professional Leagues (APL), alongside participating clubs, has had to make the decision to postpone today's A-League Women elimination final between the Central Coast Mariners and Canberra United," the APL said in a statement.
"Following extensive rain in Gosford in the last 24 hours, and up to 50mm of rain still to fall today, the water-logged pitch has been deemed unplayable.
"The match will be rescheduled to tomorrow night (Monday 28 April), kick off 6:00pm AEST, following a further pitch inspection in the morning."
Third-placed Adelaide United host sixth-placed Western United at Coopers Stadium on Sunday afternoon in the other elimination final.
The highest-ranked qualifier from the two elimination finals will face second-placed Melbourne Victory in a two-legged semi-final.
The lowest-ranked qualifier has the unenviable task of taking on unbeaten premiers Melbourne City across two legs in the other semi-final.
City were presented with the premiers plate on Saturday night.
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