Let G/K be a noncompact, rank-one, Riemannian symmetric space, and let G ރ be the universal complexification of G. We prove that a holomorphically separable, G-equivariant Riemann domain over G ރ /K ރ is necessarily univalent, provided that G is not a covering of SL(2, .)ޒ As a consequence, one obtains a univalence result for holomorphically separable, G×K -equivariant Riemann domains over G ރ . Here G×K acts on G ރ by left and right translations. The proof of such results involves a detailed study of the G-invariant complex geometry of the quotient G ރ /K ރ , including a complete classification of all its Stein G-invariant subdomains.