The robbery occurred around 3:30 a.m. in Willie Mays Plaza at Third and King streets.
The 38-year-old victim, who was apparently intoxicated, was approached by a suspect who asked him for money, according to police. When the victim pulled out his wallet, the suspect punched him, knocking him out. When he regained consciousness, he discovered his wallet was gone, police said.
The man was treated at the scene for a cut to his head but did not require hospitalization.
No arrests had been made in connection with the robbery as of this morning, police said. Anyone with information about the case is asked to call the Police Department's anonymous tip line at (415) 575-4444 or send a tip by text message to TIP411.