Both analytic and geometric forms of an optimal monotone principle for $L^p$-integral of the Green function of a simply-connected planar domain $Omega$ with rectifiable simple curve as boundary are established through a sharp one-dimensional power integral estimate of Riemann-Stieltjes type and the Huber analytic and geometric isoperimetric inequalities under finiteness of the positive part of total Gauss curvature of a conformal metric on $Omega$. Consequently, new analytic and geometric isoperimetric-type inequalities are discovered. Furthermore, when applying the geometric principle to two-dimensional Riemannian manifolds, we find fortunately that ${0,1}$-form of the induced principle is midway between Moser-Trudingers inequality and Nash-Sobolevs inequality on complete noncompact boundary-free surfaces, and yet equivalent to Nash-Sobolevs/Faber-Krahns eigenvalue/Heat-kernel-upper-bound/Log-Sobolevs inequality on the surfaces with finite total Gauss curvature and quadratic area growth.