How do you add an opportunity to an account via the API?

How do you add an opportunity to an account via the API?

The docs are clear on adding contacts, leads, and accounts via the API.  I've got that fine.  However I can't find how to add an update an opportunity to an account via the API.  Do I insert the opportunity first using the Accounts API and the insertRecords method?  What XML do I use to describe the new opportunity?

I'm surprised there isn't a doc, or I just can't find it.