Deeply bound 1s states of pi(-) in (115,119,123)Sn were preferentially observed using the Sn(d(3), He) pion-transfer reaction under the recoil-free condition. The 1s binding energies and widths were precisely determined and were used to deduce the isovector parameter of the s-wave pion-nucleus potential to be b(1) = -(0.115+/-0.007)m(pi)(-1). The observed enhancement of \b(1)\ over the free piN value (b(1)(free)/b(1) = 0.78+/-0.05) indicates a reduction of the chiral order parameter, f(pi)*(rho)(2)/f(pi)(2)approximate to0.64, at the normal nuclear density, rho=rho(0).