Understanding the mechanisms by which an invasive plant species is able to colonize and successfully expand into native plant communities can help in estimating the potential threat posed by a new invader and predict impacts on community diversity, structure, and function. Wavyleaf basketgrass [Oplismenus undulatifolius (Ard.) P. Beauv.] is a perennial, shade-tolerant grass species that has been recently introduced to the mid-Atlantic United States. Areas invaded by O. undulatifolius typically have low species richness, but it is unknown whether O. undulatifoius actively outcompetes other species or simply thrives primarily in species-poor habitats. This study used a greenhouse experiment to quantify interspecific competition in shade and sun among seedlings of O. undulatifolius; Japanese stiltgrass [Microstegium vimineum (Trin.) A. Camus], an invasive annual grass common in the region; and a mix of three native perennial grass species commonly used in restoring areas invaded by M. vimineum. In this experiment, shade did not significantly affect growth or competitive ability. Interspecific competition irrespective of shade had a negative effect on growth of all species, but O. undulatifolius was affected to a much greater degree than either M. vimineum or the native grass mix. These results suggest that, at least under these conditions, O. undulatifolius is a weak interspecific competitor and may be capable of forming dense monotypic stands only in areas that already have low species diversity. In the mid-Atlantic region, postagricultural legacies and overabundant deer populations, which lead to depauperate understories, may be a major facilitator of O. undulatifolius invasion in forests.