The pilot of the tailwheel-equipped airplane reported that during landing, while decelerating, the airplane veered left. He applied full right rudder, but there was "little to no change in the yaw" with the control stick full aft. The tailwheel had "unlocked" when it contacted the runway since the airplane was yawed to the left. He added engine power to increase airflow for better rudder effectiveness and the airplane began to straighten out, but the airplane exited the runway to the left and the right main landing gear collapsed. The airplane sustained substantial damage to the right wing lift strut. The pilot reported that there were no preaccident mechanical failures or malfunctions with the airplane that would have precluded normal operation. The airport's automated weather observation station reported that, about 5 minutes before the accident, the wind was calm. The pilot landed the airplane on runway 04.