  We propose an extension of the hard-wall AdS/QCD model by including the
Chern-Simons term required to reproduce the chiral anomaly of QCD. In the
framework of this holographic model, we study the vertex function F_{\pi
\gamma^* \gamma^*}(Q_1^2,Q_2^2) which accumulates information about the
coupling of the pion to two (in general virtual) photons. We calculate the
slope of the form factor with one real and one slightly virtual photon and show
that it is close to experimental findings. We analyze the formal limit of large
virtualities and establish that predictions of the holographic model
analytically (including nontrivial dependence on the ratio of photon
virtualities) coincide with those of perturbative QCD with asymptotic pion
distribution amplitude. We also investigate the generalized VMD structure of
F_{\pi \gamma^* \gamma^*}(Q_1^2,Q_2^2) in the extended AdS/QCD model.
