The churning phase of a grease-lubricated rolling bearing significantly impacts the aging of the grease, affecting both bearing performance and service life. Knowledge about the influence of the running-in procedure on grease aging is limited. In this article, we studied grease aging in a ball-bearing running-in process with two additive-free greases made with the same base oil but different thickeners: lithium complex and polyurea. Rheological characterization of the greases was performed after two different 48-h running-in procedures. Both procedures employed a stepwise running-in process with either increasing or decreasing speeds. The results reveal that grease aging in the bulk and near the raceway varies significantly depending on the speed procedure used. The level of aging induced by the speed procedures is thickener dependent. The polyurea grease exhibits more severe aging when subjected to a running-in procedure with sudden high speeds (decreasing speed procedure). Conversely, the lithium-complex grease is more susceptible to aging during a running-in procedure with increasing speeds. The implications of the applicability of these speed procedures in industrial and research applications are also discussed.