A novel single-cell-level phenotypic assay is described, which can simultaneously analyze HIV-1 drug susceptibility and intrinsic replication capacity. This allows quantitative dissection of the functions of antiretroviral drugs into suppression of viral replication and selection of resistant viruses with diminished replication capacities. The disclosed assay provides a tool for the rational evaluation of treatment decisions for patients failing antiretroviral therapy and is expected to be an important part in clinical management of HIV.