A disposable, all-plastic centrifuge rotor for fluid processing includes a unitary, molded plastic upper rotor portion that includes a rotor shaft spud. A unitary, molded plastic lower rotor portion is provided and is joined to the upper rotor portion so as to define a hollow rotor interior. Positioned within the hollow rotor interior is a unitary baseplate that is joined to the lower rotor portion and includes a rotor shaft spud. The rotor shaft spud of the unitary baseplate extends through the lower rotor portion and beyond the lower rotor portion and is coaxial with the rotor shaft spud of the upper rotor portion. A spiral vane element is positioned in the rotor interior and is captured between the upper rotor portion and the baseplate for fluid processing as the centrifuge rotor rotates at a high RPM rate.