Sabre will automatically break the itinerary and price more than one award if applicable. However, to help you understand the Sabre logic, the most important routing rule for award travel is:

Passenger must travel the most direct routing
When booking travel on partner airlines, the system will be applying the most direct routing rule automatically. Pricing on all partner awards may result in two awards if the most direct routing is not used. With the implementation of One-Way Flex Awards, pricing is designed to follow each carrier's routing rules. Other airline awards are based on 2 routing rules: mileage (MPM - maximum permitted miles), or specified routing (nonstop, connecting cities etc.). In order to have one-way itineraries price as one award (a.k.a. a through fare in the revenue world) we must follow the mileage or routing restrictions for each governing carrier.
You may see the system applying this rule with a little more flexibility when the governing carrier is on AA.