NEW YORK—A New York Police Department rookie just couldn’t wait to get started.

One of the NYPD’s newest officers made his first arrest Thursday just minutes after graduating from the Police Academy in a ceremony at Madison Square Garden.

Officer Dariel Firpo, 23, was leaving the midtown Manhattan ceremony when he saw a 79-year-old man being robbed of his wallet and thrown to the ground by a mugger, police said.

The mugger tried to run away, but Firpo caught him without incident, they said.

The man Firpo arrested, Jeffrey Grant, was being charged with robbery. Grant, 47, has 48 previous arrests and was just released last week from Sing Sing Correctional Facility in Ossining, N.Y., after serving time for a robbery conviction, police said.

The mugging victim was treated at a hospital for a broken wrist.

Firpo’s feat “may be the fastest police action upon graduation in department history,” said chief police spokesman Paul Browne.