A tracking problem in the presence of disturbances for a class of nonlinear systems is considered. A connection between the exponential stability of the undisturbed system and the exponential tracking property of the disturbed system is established. With this connection, a new controller and its computation scheme are proposed based on the L-2 finite gain framework. The new controller can make the closed-loop system exponentially track a step signal and attenuate disturbances. Finally, an example in process control is given to demonstrate the method.