The officer chased the fare beater as he ran from the 14th Street and Eighth Avenue subway station Wednesday evening.
Police say the suspect threw the officer to the ground and fled, leaving behind a shirt and baseball cap.
That's when Diesel, a transit K9 German shepherd, arrived. The 7-year-old pooch sniffed the clothes and headed west on 16th Street.
Diesel and Officer Edwin Ramirez then went to a second-floor of the Dream Hotel where a 32-year-old Jersey City, N.J., man was arrested. The man was charged with theft of service, resisting arrest, criminal trespass and obstructing governmental administration.
The transit officer suffered a wrist injury.