Mexico's Juan Estrada has vowed to hold onto his world crown "as long as he possibly can" as he prepares to defend his WBA and WBO titles in Saturday's Fists of Gold II bill. The 23-year-old from Sonora state in Mexico (24-2-0, 18 KOs) stunned the boxing world by becoming the new world champion after defeating flyweight great Brian Viloria of the US (32-4-0, 32 KOs) in Fists of Gold I at the CotaiArena at the Venetian hotel-resort in April. Estrada's unanimous decision against the 32-year-old American legend was huge news in his homeland and the shy Mexican will find out whether he has what it takes to retain both world title belts when he comes up against undefeated Filipino fighter Milan Melindo (29-0-0, 12 KOs) in a 12-round title bout. "It's going to be a a tough fight, but I have prepared great for it. I feel good right now and I am ready," said Estrada at yesterday's welcoming ceremony. "Beating Viloria was such a great victory … not only for me, but my team and my country." "My ambition is to stay world champion as long as I possibly can," said the Mexican who was introduced to boxing by his elder brother Luis when he was nine. Fists of Gold II will also feature another world title fight between challenger Mauricio Munoz of Argentina (26-3-0) and IBF featherweight world champion Evgeny Gradovich of Russia (16-0-0), who in March upset Australian Billy Dib for the IBF featherweight championship. Two-time Olympic gold medallist Zou Shiming of China will return to the ring in a flyweight matchup against Mexico's Jesus Ortega in his second professional fight. Undefeated Hong Kong super flyweight Rex Tso Sing-yu will face Thailand's Rusalee Samor in another bout, competing at a "catch weight" of 117 pounds, instead of his usual 115 pounds. "It's very hard to maintain a fighting weight of 115 pounds, and I will most likely fight at 117 pounds instead. We have already been given permission and there's no objection from our opponent," said recently turned 26-year-old Tso, who will be fighting at the CotaiArena for the first time. Fists of Gold II will be broadcast live to more than 30 countries, including the US via HBO 2 and China on CCTV. A spokesman for promoters Top Rank said more than 300 million were expected to watch the bouts.