An automatic transmission fluid (ATF) filtration system that combines both coarse filtering mesh and microfine depth filtering elements simultaneously to remove a wide range of particulate matter, but also maintains an unrestricted flow of ATF to the pump to ensure its volumetric efficiency is disclosed. In the present invention ATF at system pressure is delivered via a hydraulic circuit to a microfine depth filtering element for depth filtration (i.e. several layers of filter media) and, thereafter, is passed into the intake of the coarse filter element or, alternatively, between the intake of the coarse filter element and the pump intake. Because ATF flow through the coarse filter element is continuous and independent of the microfine depth filter element, the volumetric efficiency of the pump is maintained in all phases of operation even at the highest demand points such as at cold start-up, hot idle, and high volume/demand situations.