A mirror reflector sub-assembly for a vehicular exterior rearview mirror assembly includes a mirror reflective element having a glass substrate with first and second surfaces. The mirror reflective element has a principal reflector portion and an auxiliary reflector portion. The auxiliary reflector portion of the mirror reflective element includes a curved recess established at the second surface of the glass substrate by at least one of grinding and ablating. A reflector is established at the curved recess and a principal mirror reflector is established at the principal reflector portion. The mirror reflective element is supported at a side of a mirror back plate and an opposing side of the mirror back plate is configured for attaching the mirror back plate to a mirror actuator. The opposing side of the mirror back plate includes an attaching portion that snap attaches to the mirror actuator.