On May 29, 2004, after accumulating an undefeated record of 5 wins, 5 KOs, Amonsot made his international debut when he fought in unfamiliar territory in Uijeongbu, South Korea against Kim-Jung Park.
[1] After registering two wins, a draw, and his first loss as a pro in Indonesia, Amonsot came back to the Philippines to defeat Jun Paderna and Richard Cabillo.
He later went on to defeat the then undefeated WBO Asia Pacific Super Featherweight Champion Victor Mausul of Indonesia to earn his first regional belt.
[2] Amonsot won his next three fights after the win over Favela, beating the likes of Decho Kokietgym, Jose Reyes, and Silverio Ortiz, accumulating a record of 17-1-1 with 10 victories coming by way of knockout.
On July 21, 2007, Amonsot faced Katsidis for the interim WBO lightweight title at the Mandalay Bay Resort in Las Vegas, Nevada.