The victim was attacked on the north side of Washington Square Park just before 2:30 a.m.
"I've always thought after 12 a.m., kind of move out of there," an eyewitness said. "I've never seen anything that sort of scary happen, so that kind of makes you think."
The 19-year-old man was apparently smoking marijuana with two women when the two men approached him and ask for some.
He declined, and one stabbed him in the left side of the head.
The victim, from New Rochelle, was taken to Bellevue Hospital in stable condition.
Two men in their 20s were spotted fleeing the scene.
So far, no arrests have been made.
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