As a child, he sold flowers in the resort city of Pattaya to help support his younger siblings.

Like many poor boys in Thailand, he took up Muay Thai, and he proved to be a gifted boxer under the ring name "Petchpayao Sitkrutat" (เพชรพะเยาว์ ศิษย์ครูทัศน์).

He trained hard for the 1980 Moscow Olympics, but his hopes for a gold were ended by the United States led boycott over of the Soviet Union's invasion of Afghanistan.

Instead, he turned professional and on November 27, 1983 became WBC superflyweight world champion by defeating Rafael Orono of Venezuela in a split decision.

In his first title defence, against Guty Espadas of Mexico, Phayao was behind on all the score cards, but saved his championship belt with a 10th-round knockout.