Like many of the Welsh members of John Dawes' Lions side, he had a taste of what to expect in New Zealand when making Wales' ill-fated 1969 tour and coming up against a rampant All Blacks side.
But as part of a stronger Lions side two years later, and coached by Carwyn James, the tourists took New Zealand by storm, unleashing in the provincial games but playing more cautiously in the Test matches to win the series 2-1.
And his Williams' 45-metre dropped goal was the icing on their 14-11 fourth Test win that gave them their only series win over the All Blacks.
Veteran English journalist Peter Jackson recounted in the Daily Mail that on the bus to Eden Park for the series-deciding Test, Williams announced he would drop a goal in the game.
Williams said, "Everyone burst out laughing. I'd only ever dropped two goals in my life, in my first match for Bridgend against Bristol in 1967 and another for Wales against Fiji in 1969. Not surprising, really, because I always preferred to run the ball rather than kick it."
He hit the kick perfectly, admitting that fellow Lions squad fullback Bob Hiller of England put the idea in his head.
A fine defender, Williams complemented that area of his game with a willingness to join the backline to strengthen the Lions' already impressive attacking edge. While there were faster fullbacks, like New Zealand's Christian Cullen and 1977 Lion Andy Irvine, only some were as effective defensively.
He would go on to tour South Africa for another series win in 1974 and was still playing at club level for Bridgend in 1978 when suffering a facial injury from All Blacks prop John Ashworth's rucking. He left the field and was stitched up by his father, a doctor and president of the club, only to return when ignoring the advice of his father and three doctor brothers.
Carwyn James rated him 'the competitor of competitors'. He was good enough to win the British Junior tennis title in 1966. He played 55 Tests for Wales between 1969-81 and eight Tests for the Lions and was still playing club rugby in Wales in 2003, all while working as an orthopaedic surgeon.
It was while still a trainee doctor in 1971 that he came to All Blacks' first five-eighths Bob Burgess' aid after he was knocked unconscious to prevent him from swallowing his tongue after making a tackle attempt.
He was captain of the Wales side that lost 12-13 to the All Blacks when Brian McKechnie kicked a late penalty goal in the famous 'Haden lineout' Test in 1978 and also appeared in the 1980 Welsh centenary Test 3-23 loss to the All Blacks.