We consider Sauter-Schwinger pair production by electric fields that depend on both time and space, E(t; z) and E(t; x; y). For space independent fields E(t), momentum conservation δ(p + p') fixes the positron momentum p' in terms of the electron momentum p. For E(t; z), on the other hand, pz and pź are independent. However, previous exact-numerical studies have considered only the probability as a function of a single momentum variable, P(pz), P(pź) or P(pź − pz), but not the correlation P(pz; pź). In this paper, we show how to obtain P(pz; pź) by solving the Dirac equation numerically. To do so, we split the wave function into a background and a scattered wave, ψ(t; x) = ψback:(t; x) + ψscat:(t; x), where ψback: ∝ exp(±ipx + gauge term). ψscat. vanishes outside a past light cone and is obtained by solving (i= D − m)ψscat: = −(i= D − m)ψback:. backward in time starting with ψscat:(t → +∞; x) = 0.