This paper solves unsteady Reynolds-averaged Navier-Stokes (URANS) equations to simulate stall inception of NASA compressor stage 35 with rotor-stator interaction. A full annulus of the rotor-stator stage is simulated with an interpolation sliding boundary condition (BC) to resolve the rotor-stator interaction. The tip clearance is fully gridded to accurately resolve tip vortices and its effect on stall inception. The unsteady simulation indicates that the inception of rotating stall in Stage 35 is spike inception. The stall cells grow quickly and brings the rotor to full stall within roughly 1.2 revolutions. The stall cell propagates at about 90% of rotor speed in the counter rotor rotation direction in relative the frame.