Originally Posted by
lg20
From the DL site:
Delta One or SkyTeam Premium Cabin Passenger
Customers traveling in Delta One on an international Delta flight or a domestic Delta flight connecting to/from a same-day international Delta flight* in Delta One or travel in international First/Business Class on a SkyTeam-operated flight. (In order to qualify for Club access, the customer must be confirmed in the premium (first or business class) cabin for the international segment of their itinerary.)
or
Transcontinental Delta One™
Customers traveling on a nonstop Delta One ticket between New York-JFK and Los Angeles or San Francisco.
D1 is business class, not FC. The OP specifically talked about a FC ticket.
I don't think DL serves Mexico, Central America, or northern South America from SEA, so that leaves the transborder Canadian flights as eligible for SC use with a FC ticket.