In order to reduce the memory requirements of quantum reactive scattering calculations based on delocalized basis sets, we use a discrete basis in a single interaction region coordinate system, resulting in a sparse Hamiltonian matrix. The resulting set of linear equations is solved via an iterative method which exploits their sparsity. Other important features of our formalism are the use of a truncated grid and distorted waves used to shrink the interaction region, and therefore the basis size. We demonstrate the method and assess its efficiency for the reaction D+H-2 --> DH+H, at a total energy of 0.9 eV and zero total angular momentum (J=0).