Primary piston assembly (22, 28) for a master brake cylinder of a brake system of a vehicle, having: a first primary piston component with a first piston part to which, via a first force transmission contact between the first primary piston component and at least one brake actuation element arranged on the brake system, a driver-imparted braking force (Fb) can be transmitted such that, as a result of an adjustment of the first piston part by means of the driver-imparted braking force (Fb), a liquid-fillable pressure chamber volume of a pressure chamber of a master brake cylinder of the brake system can be reduced; and a second primary piston component with a second piston part to which, via a second force transmission contact between the second primary piston component and at least one brake force booster actuator device, a first braking assistance force provided by the brake force booster actuator device can be transmitted such that, as a result of an adjustment of the second piston part by means of the first braking assistance force, the liquid-fillable pressure chamber volume of the pressure chamber can be additionally reduced; wherein the first piston part has a through aperture within which the second piston part is at least partially arranged in adjustable fashion, and wherein, as a result of the adjustment of the first piston component by means of the driver-imparted braking force (Fb), at least one breather bore (38, 40) of the master brake cylinder can be sealed off, characterized in that a first end section, directed away from the first piston part, of the first primary piston component projects into an interior space which is spanned by at least one second end section, directed away from the at least one second piston part, of the second primary piston component. a first primary piston component with a first piston part to which, via a first force transmission contact between the first primary piston component and at least one brake actuation element arranged on the brake system, a driver-imparted braking force (Fb) can be transmitted such that, as a result of an adjustment of the first piston part by means of the driver-imparted braking force (Fb), a liquid-fillable pressure chamber volume of a pressure chamber of a master brake cylinder of the brake system can be reduced; and a second primary piston component with a second piston part to which, via a second force transmission contact between the second primary piston component and at least one brake force booster actuator device, a first braking assistance force provided by the brake force booster actuator device can be transmitted such that, as a result of an adjustment of the second piston part by means of the first braking assistance force, the liquid-fillable pressure chamber volume of the pressure chamber can be additionally reduced; wherein the first piston part has a through aperture within which the second piston part is at least partially arranged in adjustable fashion, and wherein, as a result of the adjustment of the first piston component by means of the driver-imparted braking force (Fb), at least one breather bore (38, 40) of the master brake cylinder can be sealed off, characterized in that a first end section, directed away from the first piston part, of the first primary piston component projects into an interior space which is spanned by at least one second end section, directed away from the at least one second piston part, of the second primary piston component.