Burstiness (i.e., sudden surges) in user demands in enterprise systems that operate under the multi-tiered paradigm is a common phenomenon that leads to overprovisioning: the system is configured with excess hardware to meet peak user demands, often resulting in excessive (and unnecessary) power costs. In this paper, we present Fastrack, a parameter-free algorithm for dynamic resource provisioning that uses simple statistics to promptly distill information about changes in workload burstiness. This information, coupled with the application's end-to-end response times and system bottleneck characteristics, guides resource allocation, which proves to be effective under a broad variety of application burstiness profiles and bottleneck scenarios. Extensive simulations illustrate Fastrack's robustness for consistently meeting predefined service level objectives while minimizing power usage.