It's the second year in a row the winner has been the youngest in the history of the event, which has been around since 1895 and played 109 times.
A 17-year-old born in South Korea, An took a 3 up lead by winning three of the last four holes in the pairing's first of two 18-hole rounds Sunday. He doubled that edge as Martin bogeyed five of the first seven holes in the afternoon round.
An is about a month and a half younger than Danny Lee was when he broke Tiger Woods' record last year to become the U.S. Amateur's youngest champion. Lee was 18 years, 1 month old at the time of his victory.