We study gravitational perturbations of Schwarzschild-AdS black holes in $\textit{d}$ = 5 and identify a regime of late-time power-law decay for smooth initial data. Based on an analysis of the quasinormal mode spectrum, we predict and characterise this decay behaviour. We perform fully nonlinear numerical evolutions with long integration times that support the prediction and exhibit no signs of instability. Remarkably, the decay is modulated by a universal oscillatory pattern, consistent with subleading corrections from a large-angular-momentum (eikonal) analysis of the quasinormal mode spectrum.