An extension of the Pade method is made introducing a two-step approximant as suggested by the biorthogonal algorithm considered in a previous work. In this way we have a new tool for the analytic continuation of power series. The two-step approximant is particularly useful in the cases where the usual Pade method does not work, for example, the total T-matrix and the half off-shell partial-wave amplitude. The full off-shell extension of the two-body amplitude is considered and a process is developed to obtain separable forms.