The stabbing was reported at about 8 p.m. Saturday near the intersection of 23rd Street and Potrero Avenue.
The 25-year-old victim was approached from behind by the suspect, who cut him in the neck, according to police.
The victim was taken to a hospital to be treated for his injuries, which are not considered life-threatening, police said.
The suspect fled and had not been found as of Monday. A detailed description of the suspect was not immediately available.
Anyone with information about the stabbing is encouraged to call the Police Department's anonymous tip line at (415) 575-4444 or send a tip by text message to TIP411.