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.
"Officer Firpo made us all proud," police Commissioner Raymond Kelly said. "He's off to a great start."
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.
Hope the creep does time. Breaking an old man's wrist while you are trying to rob him is not cool.