A cop in Times Square was knocked out shortly after 10 a.m. yesterday when he was trying to arrest a fare evader, police said.

The cop had approached the suspected turnstile jumper at the 42nd Street stop on the Eighth Avenue line and tried to arrest him. The cop radioed for backup.

When officers arrived, they allegedly saw the suspect on top of the cop, apparently choking him.

Police said the cop lost consciousness after suffering a head injury and was taken to New York Hospital, where he was listed in stable condition.

Cops arrested Daniel Walker, 19, of Lenox Avenue and charged him with assault, fare evasion, resisting arrest and criminal trespass.