Contact growth and temperature behavior in time during a single high-current pulse representing the initial stage of field-assisted/spark plasma sintering (FAST/SPS) have been studied experimentally and numerically. The measured evolution of the electrical resistance and of the neck formation process in two-particle systems is compared to the results obtained from the fully coupled thermo-electro-mechanical finite element simulations. The results of simulations with various models of inelastic deformation show that the viscoelastic/viscoplastic material model provides a realistic contact growth in initial stage of FAST/SPS. The impact of electrical and mechanical loads, material parameters and particle size on temperature, on inelastic strain distribution and on densification has been studied by finite element simulations for copper, stainless steel and nickel particles.