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He now has four more centuries than the next best, Ross Taylor, who scored 70 on the first day of this test. The late Martin Crowe has 17 while Brendon McCullum and John Wright round out the top five with 12 apiece.
The New Zealand captain started the day on 94 and needed 25 minutes to score his first runs, a scuffed leg glance for two.
He went to three figures with a trademark checked drive through the covers off Naseem Shah.
His century took him 261 balls, very slow by his standards, but necessary.
Henry Nicholls, fresh off his highest test score in the second test against the West Indies, was with him at the crease on 52, his 10th test half-century, which he will be aiming to convert into his seventh test ton.
The pair had put on 106 for the fourth wicket and New Zealand were well placed at 239-3.
It is Williamson's first test innings and first century as a dad, with wife Sarah having given birth earlier this month, an event that saw him miss the second test against the West Indies.
It is just the second time he has scored centuries in back-to-back innings.
The only other time he did it was when he scored 242 not out against Sri Lanka at the Basin Reserve in January 2015, then backed it up with a high-class 132 at Lord's in May that year.
In many ways it mirrored his 22nd century in that he reached stumps on day one within a single shot of his milestone, having spent the majority of the day in a battle of attrition with the bowlers.
If anything, the struggle here was greater than it was against the West Indies in Hamilton. Although the pitch conditions were not quite as weighted in the bowlers' favour as they were at Seddon Park, here the attack led by 20-year-old left-armer Shaheen Shah Afridi was more skilful and relentless.
"It's just Kane, isnt it? He batted very well. It was good to bat with him and get through that initial stage," said Taylor when asked to analyse Williamson's day one performance.
"He batted all day pretty much, apart from three balls. The temperament, the timing, obviously you need a little bit of luck here and there but I thought he batted fantastically well."
Williamson leaves legends of game Wally Hammond, Colin Cowdrey, Geoff Boycott, Ian Bell, AB de Villiers and Mohammad Azharuddin behind on 22 and joins a select group that includes Javed Miandad, Justin Langer, Kevin Pietersen and Virender Sehwag.
The difference is all those players have topped 100 tests. This is Williamson's 82nd.
Only 26 players in the in the 143-year history of test cricket have reached three figures more than Williamson.
He scores a century 16.2 per cent of the time he comes to the crease, good enough for 13th best. Of the current players, only Steve Smith (19.5) and Virat Kohli (18.4) convert more of their innings to 100s.
The incomparable Don Bradman leads the way with a ridiculous 36.25 percent.