How axial anomaly manifests itself at the chiral phase transition temperature affects the nature of chiral phase transition and it is a fundamental question in QCD. We performed a first continuum and chiral extrapolation of two UA(1)UA(1) measures in (2+1)-flavor lattice QCD at T=205T=205 MeV. By using the proposed novel relations between the quark mass derivatives of Dirac eigenvalue spectrum ρρ and correlation functions among eigenvalues we find that the microscopic origin of the current manifested axial anomaly is the peak structure developed in ρρ with its height proportional to quark mass squared. These strongly suggest the chiral phase transition belongs to 3-d O(4) universality class.