He said the surf was so rough about 2.40pm off Loma Park that the two men vanished within seconds.
Khun Sakon pulled out one of the youngsters but the other disappeared. Khun Sakon plunged to their rescue so quickly he forgot that he had a mobile telephone in a pocket.
The hunt for the body of the young man will resume today.
''It was very bad surf,'' Khun Sakon said. ''There were seven in the group.
''I am told the young man's mother works in Patong, and that he came from Bangkok to visit her.
''The man I pulled out was aged 22. His friend was aged 17 or 18.''
Along the beach a bit further, Khun Sakon said, waves tipped over a jet-ski, meaning the hirer will probably have to pay to recondition the engine.
''The beach slopes away steeply so an inexperienced swimmer will quickly be out of their depth when it is this rough,'' he said.
Thunderstorms and strong surf conditions are predicted through until Thursday.
Other drownings or deaths associated with a collapse in the water have been recorded since May 18 at Karon, Freedom Beach and Nai Harn.