The stabbing occurred around 6 p.m. near 22nd and Bartlett streets.
The 33-year-old victim was standing on the sidewalk when the suspect stabbed him on the left side of his torso, according to police.
The victim went to San Francisco General Hospital to be treated for his injuries, which are considered life-threatening, police said.
The suspect, described as a man in his 30s, fled and had not been found as of this morning, according to police.
Anyone with information about the stabbing is asked to call the Police Department's anonymous tip line at (415) 575-4444 or send a tip by text message to TIP411.
