A pivotal bone anchor assembly includes a bone anchor having a capture portion and an anchor portion opposite the capture portion, and a receiver assembly in a pre-assembled configuration that includes a receiver, a retainer, and a pressure insert. The receiver has a central bore configured to receive the capture portion through a bottom opening, with a lower portion of the central bore including a narrower engagement portion adjacent the bottom opening and a wider expansion portion above the narrower engagement portion. The pre-assembled retainer is configured to widen within the wider expansion portion to receive the capture portion of the bone anchor during its uploading through the bottom opening, then to close around and secure the capture portion while providing for pivotal motion of the bone anchor relative to the receiver. The pre-assembled insert is downwardly deployable with tooling, prior to the installation of a longitudinal connecting member and closure, until an outer surface of the insert comes into forced interference wedged engagement with interference wedging surfaces formed into the central bore so as to inhibit the pressure insert from moving back up within the receiver.