To deal with complex nonlinear systems such as underactuated mechanisms, in this paper a global stable as well as optimal fuzzy controller is presented to achieve output tracking control of nonlinear systems by combining the linear optimal control theory and linear regulator theory with the Takagi-Sugeno fuzzy methodology. The stability of the entire closed-loop fuzzy system is ensured by the Lyapunov stability analysis. This paper also includes a hardware description and the real-time results for the application to a benchmark underactuated robot: Pendubot.