An exterior sideview mirror assembly includes a single mirror backing plate element within a mirror housing. A main plano mirror element and an auxiliary non-plano curved mirror element are supported by the backing plate element. The backing plate element has a generally flat portion for supporting the main plano mirror element and a curved portion for supporting the auxiliary non-plano curved mirror element. The curved portion may be angled relative to the generally flat portion in a manner such that, when a driver of the vehicle aligns the rearward field of view of the main plano mirror element, the rearward field of view of the main plano mirror element may be aligned downwardly relative to the vehicle body side. The main plano mirror element includes a generally flat reflector-coated glass substrate or a generally flat polymeric substrate having a thin glass element applied to a surface thereof.