If you call DL and pay the phone ticketing fee, IIRC $25, you can have a single ticket with some segments in FC and some in coach. How about FC outbound and coach on the return in your case? Or even just ATL-SAN in FC to maybe save more money?

Having two tickets, even if linked, and no status could lead to big trouble if your first flight is cancelled, rescheduled, or delayed.

Welcome to FT.

BTW, if your ticket might be at least partially reimbursed, you should look at the organization's rules and re-think your strategy. Having paid FC could cause trouble.