Make sure that your records also have an auto-entered serial number field. If you need to add such a field, use Replace Field Contents to give each of your existing records a serial number while you have a found set of all records in Unsorted order.
Use a second occurrence of your portal's table and link it to the portal's table occurrence like this:
PortalTO::NameField = PortalTO 2::NameField
Use this as your portal filter expression:
PortalTO::SerialNumber = Min ( PortalTO 2::SerialNumber )