Buffelgrass (Pennisetum ciliare (L.) Link), a C4 perennial bunchgrass native to Africa and parts of Asia, has invaded broadly across the southwestern United States and northern Mexico. Buffelgrass establishment may occur earlier than the natives it displaces which may preempt resource acquisition by native species and contribute to its invasion success. In a greenhouse, buffelgrass aboveground growth was tested against Arizona cottontop (Digitaria californica (Benth.) Henr.), a native C4 perennial bunchgrass, in pairwise combinations in a randomized complete block factorial design with 10 replications, three neighbor identities (self, other, and no neighbor), and three competition treatments (21-day younger neighbor, 21-day older neighbor, and same-aged neighbor). When compared with control plants, there was no significant effect on aboveground biomass for older Arizona cottontop plants competing with younger buffelgrass plants (p > 0.05). However, when Arizona cottontop plants were of the same age or younger than buffelgrass plants, buffelgrass caused 95 and 88% reductions, respectively, in aboveground biomass (p < 0.05 in both cases). Intraspecific competition between same-aged Arizona cottontop plants resulted in only 55% decline in aboveground biomass production (p < 0.05), thus interspecific competition with buffelgrass was more intense than intraspecific competition for Arizona cottontop when plants had similar emergence times. These results suggest that establishing native plants immediately following a disturbance event could be a practical technique for restoring or retaining diversity on sites with high potential for invasion by buffelgrass.