Just to be clear on this. As a oneworld sapphire member on a oneworld marketed and operated international* flight you are entitled to use ANY oneworld business class lounge, save where the lounge is full, or is operated by a third party, or certain QR lounges. I strongly suggest you print out the access rules and take them with you. There are plenty of stories of undertrained lounge receptionists refusing entry on the basis of misunderstanding the rules. If you are able to point to the rules, it is going to be tough for them to refuse you entry.
I often use oneworld lounges which are not those of the carrier I am flying. For example, although I am a CX FF and fly CX to these destinations, I would generally use the AA lounge at NRT, the BA lounge at LHR and the QF lounge at SIN. I have not yet had a problem.
* I include the word international here since you derive your oneworld status from AA, and like QF they do not give lounge access based on status for domestic flights.