We address the problem of trajectory tracking control of a quadrotor-slung-load system. A novel control framework is proposed that relaxes the differentiability class order of the reference. In lieu of traditional approaches that primarily regard the position of either the quadrotor or the load in the design of tracking controllers, in this work, we consider a virtual point located along the cable between the vehicle and the payload. The resulting control framework, which draws parallels with a typical single quadrotor dynamic system, is characterized by an utmost simplicity since it relies only on three error variables, and requires only up to the third time derivative of the reference trajectory. The overall control scheme ensures almost global asymptotic stability of the closed-loop system in the presence of constant external disturbances. Extensive experimental results featuring time-varying exogenous perturbations are presented to validate and illustrate the effectiveness of the proposed method.