A method is provided for operating an air-staged diffusion nozzle for a gas turbine combustor to cool the nozzle tip and improve mixing of gas fuel and air within a downstream burner space. Air is mixed with the gas-fuel in an outer swirler and expanded in a downstream burner tube space. Compressed air from a cooling air cavity in the nozzle flows through an inner swirler, passing downstream from the tip of the nozzle to the burner tube space, cooling the nozzle tip and improving the mixing of the gas-fuel with air, thereby reducing emissions from the gas turbine and reducing soot formation in startup. Direction and rotation of the discharged air from the nozzle tip into the burner space may be arranged to promote nozzle tip cooling and gas-fuel mixing with air.