Assortative mate preferences (i.e. the tendency to mate with phenotypically similar individuals) are widespread in animals and are hypothesized to facilitate speciation by limiting gene flow among diverging populations. However, male-male competition can either reinforce or suppress the expression of mate preferences. Therefore, it is essential to quantify the combined effect of both mate choice and intrasexual competition on mating patterns when studying the evolution of reproductive isolation. The strawberry poison frog (Oophaga pumilio) is a highly color polymorphic species at an early stage of divergence. Females generally prefer males of the same color morph, and this assortative pattern has been interpreted as a support for speciation via sexual selection. However, this inference does not account for male-male competition. We experimentally tested the relative importance and interaction of female preference and male-male competition. Females were housed with two size-matched, differently-colored males. We manipulated male territoriality so that the female’s preferred phenotype is either the territory winner or the loser in the enclosure. These trios were kept together until one pair produced tadpoles, which we then genotyped to reveal paternity as direct evidence of reproductive success. Females mated assortatively when her preferred phenotype was the territory winner, but not when her preferred phenotype was the loser. This supports the hypothesis that male territorial status is a stronger driver of mating pattern than female color preference. Our results highlight the interaction between mate choice and intrasexual competition, and the importance to consider the combined effect of both selective forces in shaping phenotypic divergence and speciation.