A wonderful test century at Lord's, which should have been the catalyst for victory but instead became the only one of his 10 centuries to come in a losing effort, turned out to be an entrée for an astonishing ODI series.
Scores of 45, 93, 118 and 90 add up to 346 runs in just 314 balls with barely an ugly swipe among them. He has the opportunity to add to that tally in tonight's final ODI at Chester-le-Street.
There's a stat that puts Williamson's deeds in an even better light.
Of the New Zealanders to score more than 10 international centuries (there are not many of them), Williamson had the greatest ratio of innings to centuries in both test and ODIs, which demonstrates his class and ability to adapt.
To be fair to Ross Taylor, his numbers are exceptional, too, but he is smack-bang in the middle of his peak years, while Williamson is still, if conventional wisdom is anything to go by, three years from entering his.
Williamson would not have the slightest clue about this. He has no idea what his Cricinfo Statsguru page looks like. He refuses to let his career be driven by stats, even if he starts knocking down records all over the show.
"There has been success and failure and there'll be plenty more of both," he told Cricket Monthly. "You can't hold on to success for too long or hold on to failure. You've got to let both go. It's easy to fall into the trap of getting a hundred and it felt good so you want and expect more, or you fail and you don't know why and you fall into a trap.
"You want success too badly. Sometimes you have to accept you're going to have both and neither will last forever. Let them come and go."
While cricket may sometimes be dismissively described as an individual sport in a team context, for Williamson "team" is everything. He says it with such earnestness it is impossible not to be swayed by his conviction.
"[Individual records are] not why I play," he says. "Playing for the team situation is the most important thing, contributing to the team. That's for me what makes the game so much more enjoyable. You can enjoy others' success much more when you do play for these reasons.
"Sorry, there's no right or wrong reasons, but that's why I play the game that way as opposed to judging yourself on a knife-edge every day based on [stats]."
That selection knife-edge has now been blunted to the point where it is inconceivable that New Zealand would send out a side in whites or colours without Williamson at No 3.
In Williamson and Taylor, New Zealand have their best ever No 3-4 combination, surpassing the Jones-Crowe combination that underpinned New Zealand's efforts through the late-80s and early-90s.
Crowe, the man considered by most to be New Zealand's greatest batsman, has anointed him as his successor to that title, but according to Doug Bracewell, who grew up in Tauranga playing with and against Williamson, he does not need this sort of external motivation.
"I remember bowling to him once and just thinking, 'Jesus, how good is this kid?' We were in all the age-group tournaments together and we had an annual tournament that we went to every year. I reckon he went two or three years without being dismissed. The only time he wasn't batting was when they retired him," Bracewell told the magazine. "He wasn't like other kids. They played for fun but Kane played for a different reason - he played to succeed. That was how he had fun."
And right there we might have the continuing essence of Williamson's success. He clearly has talent (although he does not see himself as exceptionally talented), he clearly had a great upbringing in a supportive, sports-mad family and he clearly has a personality built to combat the highs and lows that high-performance sport can throw at you.
But perhaps the truly important thing is that, for him, scoring runs has always been a hell of a lot of fun. As long as that continues, there should be plenty more of them to come.
