At Maindy Stadium the 24-year-old featherweight faced off against the champion, experienced Italian Alberto Serti.
The 30-year-old had won the belt from Gracieux Lamperti the previous year, but this was his first defence, and he had never won a fight outside his homeland.
The outdoor Cardiff arena filled with 10,000 of Winstone’s adoring fans would have been a daunting enough prospect for Serti, but in Winstone he was facing one of the greatest fighters Wales has ever produced.
The Merthyr man had won Empire Games gold in 1958 in Cardiff, and turned professional soon afterwards. He built a remarkable winning run that saw him claim the British title from Olympic golden boy Terry Spinks in a memorable 1961 showdown.
American Leroy Jeffrey handed him his first defeat, but Winstone resolved to bounce back stronger and an April 1963 stoppage of Lamperti helped set up the Serti bout.
The champion put on a brave show, but was outclassed by Winstone who finally ended the bout with just five seconds remaining of the 14th round.
I’m not aware of any surviving video of the fight, but there’s highlights of Winstone’s 1965 defence of the European crown against Yves Desmarets in Rome in the clip below (two minutes in).
Few suspected that it would take him until 1968 to achieve that ambition, but he ran into his own personal nemesis in Vicente Saldivar.
The great Mexican triumphed in all three bouts of his trilogy against Winstone, but when he retired the Welshman claimed the vacant title by stopping Mitsunori Seki.