The goals of this study were to investigate the developmental patterns of acquisition of the Spanish tap and trill by L1 Mandarin–L2 English–L3 Spanish speakers, and to examine the extent to which the L1 and the L2 influenced the L3 productions. Twenty L1 Mandarin–L2 English–L3 Spanish speakers performed a reading task that elicited production of rhotics from the speakers’ L3 Spanish, L2 English, and L1 Mandarin, as well as the L2 English flap. The least proficient speakers produced a single substitution initially, generally [l]. The same non-target segment was produced for both rhotics, mirroring the results of previous studies investigating L1 English–L2 Spanish speakers, indicating that this may be a universal simplification strategy. In contrast to previous work on L1 English speakers, the L1 Mandarin–L2 English–L3 Spanish speakers who had acquired the tap did not tend to use it as the primary substitute for the trill. Overall, the L1 was a stronger source of cross-linguistic influence. Nonetheless, evidence of positive and negative L2 transfer was also found. The L2 flap allophone facilitated acquisition of the L3 tap, whereas non-target productions of the L2 /ɹ/ were also observed, revealing that both previously learned languages were possible sources of cross-linguistic influence.