A centrifugal method, and corresponding system, for processing blood to collect platelet rich plasma. A separation chamber is filled with blood from a fill syringe by rotating the separation chamber at a fill rotation rate and pumping the blood from the fill syringe. A soft spin is used to initially separate red blood cells from platelets by spinning the separation chamber at a soft spin rate. A percentage of the blood is drawn from the separation chamber back into the fill syringe to remove separated red blood cells. A second portion of the separated blood is drawn from the separation chamber until a red blood cell/platelet interface is detected. A hard spin is performed by spinning the separation chamber at a higher rate and connecting tubing is cleared of red blood cells by drawing a predetermined clearing volume. The platelet rich plasma is then collected in the collection syringe.