When more than one closely related plant species share the same pollination niche, reproductive interference (RI) via interspecific pollen transfer should limit their coexistence. However, some studies have reported the sympatric coexistence of two native close-relatives pollinated by the same pollinators under RI without niche partitioning. To clarify the mechanisms promoting the coexistence of species sharing pollinators, we examined the frequency dependency of RI in natural conditions and the potential roles of autonomous selfing in mitigating the negative RI effects between congeneric species. We investigated sympatrically growing Commelina communis (Cc) and C. c. f. ciliata (Ccfc) populations. These species exhibit very large overlaps in habitat preference and pollination niche, but seldom produce hybrids. First, we conducted a hand-pollination experiment to examine the negative effects of heterospecific pollen deposition (HPD) on seed production and the potential of self-pollination to mitigate the effects. We then examined the RI effects on reproductive success and the potential for autonomous selfing in the field. We found significant negative HPD effects on seed production and the mitigation effects of prior and competing self-pollination, in both Cc and Ccfc. For both species in the field, intraspecific pollinator movements and reproductive success significantly decreased with an increase in the relative floral abundance of competing species, although the negative RI effect on reproductive success was lower in Cc than in Ccfc. This could be explained by the greater potential for prior autonomous selfing in Cc than in Ccfc. Our findings suggest that Cc flowers were less affected by RI from competing species, which was likely due to a higher prior selfing ability compared to Ccfc flowers. The slight asymmetry in RI may explain the Cc-biased distribution in the study area. The study improves our understanding that prior autonomous selfing could reduce the negative RI effect from competing species and assure reproduction in mixed-mating species with frequent pollinator visitations.