He went on to break this time in Antwerp on 30 May1969 by more than a minute, this time stood as the world best for nearly another 12 years. His personal best time of 2:08:33.6 is still a world class marathon time. Clayton represented Australia at the 1968 Summer Olympics in Mexico City, finishing in 7th place (2:27:23). Four years later he ended up in 13th position (2:19:49) in the same event.