A method separates blood by centrifugation in a rotating chamber into a first separated blood component, a residual blood fluid, and an interface between the first separated blood component and the residual blood fluid. The method withdraws the first separated blood component out of the rotating chamber through a first outlet port, and also withdraws the residual blood fluid out of the rotating chamber through a second outlet port. During the separating step, the method accumulates a second separated blood component in the interface without withdrawal from the rotating chamber by monitoring the location of the interface within the rotating chamber and maintaining the interface at a location spaced away from flow communication with both the first and second outlet pods. After a selected time period, the method shifts the location of the interface within the rotating chamber into flow communication with a selected outlet port and withdraws the second separated blood component from the rotating chamber through the selected outlet port.