The correct answer is Rivaroxaban.

Direct oral anticoagulants (DOACs) are a class of medications used to prevent and treat thromboembolic disorders. They work by specifically targeting components of the coagulation cascade. Among these:

- Apixaban and Rivaroxaban are direct Factor Xa inhibitors, which means they inhibit the activity of Factor Xa, a key enzyme that converts prothrombin to thrombin and plays a central role in clot formation.
- Dabigatran is a direct thrombin (Factor IIa) inhibitor, which works by directly blocking thrombin, the enzyme responsible for converting fibrinogen to fibrin, a critical step in clot stabilization.
- Warfarin is a vitamin K antagonist that indirectly inhibits the synthesis of several vitamin K-dependent clotting factors, including Factors II, VII, IX, and X, but it is not a direct inhibitor of Factor Xa.

While both Apixaban and Rivaroxaban inhibit Factor Xa, the question asks for the direct oral anticoagulant that specifically inhibits Factor Xa. Since both are Factor Xa inhibitors, it is important to note that Rivaroxaban was the first approved DOAC of this type and is widely recognized for this mechanism.

Therefore, the most precise answer from the given options is Rivaroxaban.

Reference: Harrison's Principles of Internal Medicine, 20th Edition, Volume 2, Chapter 271, Page 2315