The 51-year-old victim was stabbed on the mezzanine level of the 125th St station just after 6 a.m.
The man was in a dispute with the suspect before he was stabbed.
The suspect first menaced the victim with a broken umbrella handle. The victim was armed with a knife, but dropped it.
The suspect then picked up the dropped knife and stabbed the victim with it, in the back and shoulder.
The victim was taken to Harlem Hospital and is expected to survived.
The broken umbrella handle was recovered at the scene. The knife was not recovered.
The victim and suspect may know each other. No arrests were immediately made.
Northbound 2 and 3 trains were bypassing 125 St as the NYPD investigated.
The incident came one day after another violent subway slashing that was caught on camera on the Upper East Side.
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