As an approximation to SDSCI [static-dynamic-static (SDS) configuration interaction (CI), a minimal MRCI; Theor. Chem. Acc. 2014, 133, 1481], SDSPT2 [Mol. Phys. 2017, 115, 2696] is a CI-like multireference (MR) second-order perturbation theory (PT2) that treats single and multiple roots in the same manner. This feature permits the use of configuration selection over a large complete active space (CAS) P to end up with a much reduced reference space P̃, which is connected only with a small portion (Q̃1) of the full first-order interacting space Q connected to P. The most expensive portion of the reduced interacting Q̃1 space (which involves three active orbitals) can further be truncated by partially bypassing its generation followed by an integral-based cutoff. With marginal loss of accuracy, the selection-truncation procedure, along with an efficient evaluation and storage of internal contraction coefficients, renders SDSPT2s (SDSPT2 with selection) applicable to systems that cannot be handled by the parent CAS-based SDSPT2, as demonstrated by several challenging showcases.