This paper presents a robust control for an underactuated Autonomous Underwater Vehicle (AUV) to track a predefined trajectory in horizontal plane. The AUV is uncontrollable in sway direction. First, the tracking error expressed in the earth-fixed frame is transformed into an introduced tracking error, so that the tracking error can be converged by using only force in surge direction and moment in yaw direction. Then, a unity gain, low pass filter is used to converge the introduced tracing error to zero and compensate the effect of added mass and hydrodynamic damping force acting on the AUV system. Tracking performance of the proposed controller is demonstrated via simulations for straight-line trajectory, circular trajectory, and sinusoidal trajectory.