The spontaneous formation of ordered spatial concentration patterns in an unstirred chemical medium, supported by dissipation of chemical free energy, has been considered often since a pioneering suggestion by Turing and early work by Prigogine et al. and more recent work by Ross et al. involving nonequilibrium thermodynamics. The prototype experimental example is the oscillatory Belousov–Zhabotinsky reaction, in which target patterns of outward-moving concentric rings are readily observed. One widely-studied question is whether “microscopic” fluctuations can nucleate these target centers, or whether a catalytic, nucleating heterogeneous center is required. Vidal and Pagola observed spontaneous initiation with no nucleating particles visible at 6-micron resolution; however Zhang, Förster, and Ross argued theoretically that this is impossible in regimes far from Hopf bifurcations. We describe here an explicit mechanism in a “supercritical regime,” following and near to the low-f Hopf bifurcation in a generalized Oregonator model, by which microscopic fluctuations can nucleate activity, and reconcile these results with Zhang et al. Concentrations remain very close to the unstable steady-state values after the system slowly passes through the bifurcation point but before occurrence of the inevitable transition to large-amplitude limit cycle oscillations. Suitably timed small (even microscopic) fluctuations about this supercritical state can sharply accelerate the inevitable onset of large-amplitude limit cycle oscillations, potentially nucleating targets.