  We analyze the statistical properties of the spectrum of the QCD Dirac
operator at low energy in a finite box of volume $L^4$ by means of partially
quenched Chiral Perturbation Theory (pqChPT), a low-energy effective field
theory based on the symmetries of QCD. We derive the two-point spectral
correlation function from the discontinuity of the chiral susceptibility. For
eigenvalues much smaller than $E_c=F^2/\Sigma L^2$, where $F$ is the pion decay
constant and $\Sigma$ is the absolute value of the quark condensate, our result
for the two-point correlation function coincides with the result previously
obtained from chiral Random Matrix Theory (chRMT). The departure from the chRMT
result above that scale is described by the contribution of the nonzero
momentum modes. In terms of the variance of the number of eigenvalues in an
interval containing $n$ eigenvalues on average, it results in a crossover from
a $\log n$-behavior to a $n^2 \log n$-behavior.
