A fuel injection system includes a plurality of mechanical unit pumps, each of which has a pump outlet. A pressure-intensifying hydraulically-actuated electronically-controlled fuel injector is provided for each of the plurality of mechanical unit pumps. Each of the fuel injectors has a direct control needle valve and an injector body that defines an actuation fluid inlet, a fuel inlet, an actuation fluid cavity and a fuel pressurization chamber. Each fuel injector also includes a moveable pumping element with a large hydraulic surface exposed to fluid pressure in the actuation fluid cavity, and a small hydraulic surface exposed to fluid pressure in the fuel pressurization chamber. An actuation fluid supply line is provided for each of the plurality of mechanical unit pumps. Each supply line has one end connected to one pump outlet and an other end connected to one actuation fluid inlet of an individual fuel injector.