رَأَيْتُ زَيْدًا — I saw Zayd.
رَأَيْتُ: past-tense verb; attached تُ is the subject pronoun in the nominative position.
زَيْدًا: direct object, accusative, bearing an overt fatḥa and tanwīn.
Proper-name status does not remove ordinary case endings from this fully declinable noun.