The coupling between photons and lattice plasmons in metallic nanostructure arrays makes them good candidates to build radiative surface plasmon polariton (SPP) lasers. We report lasing action from the defect state in a second-order distributed feedback SPP cavity. In this device, a silver nanoslit array confines the SPPs in its second-order bandgap, while a phase shift section in the array introduces a high-qualityfactor defect state for SPP lasing. At the same time, the fundamental order grating diffraction of the nanoslit array provides a high extraction efficiency from SPPs to photons. Using optical pumping, we demonstrate pulsed lasing at room temperature, with a collimated emission in the surface-normal direction and a high single-mode fiber coupling efficiency. Together with its compact two-dimensional geometry and lasing wavelength tunability, the proposed device is a promising candidate for small footprint and low-cost surface-emitting lasers.