Is it possible to use the Account.Id (or the primary key (=Id) field of the updated table in general) as the match key when running an update via the bulk API?

If yes, how to do so since the tests i've done with a simple CSV file with 2 columns failed (header looked like this: Id,Name)
The status message on the batch entry shows : "InvalidBatch:  Field name not found : Id"
As if it could not find the Id column in Salesforce's Account table.

Please advise