A 33-year-old man was randomly punched in the face — and then stabbed when he tried to defend himself — at a Greenwich Village subway station, cops said. 

The victim was sitting on a bench at the Christopher Street 1 train station around 8:10 p.m. Thursday when another man suddenly approached and socked him, cops said. 

He tried to fight back, until witnesses separated the pair, police said. 

After the struggle, the victim felt pain and realized he had been stabbed in the stomach, police said. 

He was taken to Lenox Hill Hospital in stable condition. 

The suspect — who cops described as between 20 and 30 years old, around 5-foot-7 with a slim build, last seen wearing a gray hoodie and black pants — was still on the loose Friday morning.