The ball was bobbled and non-striker Henry Nicholls called him through to history.
He was congratulated by Nicholls, before removing his helmet and offering a stoic raise of the bat to an applauding crowd.
The New Zealand captain began the second afternoon nine runs short of breaking the deadlock between himself, Ross Taylor and the late Martin Crowe as the first Kiwi cricketer to reach 18 test tons.
He straight drove Stuart Broad for four to re-open his account in overcast conditions, then made his next four runs from three scoring shots between mid-wicket and square leg before he grasped the moment.
Crowe made his last test century, 115, on July 5, 1994 against England at Old Trafford.
However, he has held – and shared since Williamson and Taylor's feats - the national record since he made his eighth ton against Australia at Adelaide on December 12, 1987, passing Glenn Turner and Bevan Congdon.
Twenty years, three months and 11 days later we have seen a changing of the guard.
Williamson’s milestone is the next step in a test career that began as the eighth New Zealander to make a hundred on debut with 131 on November 7, 2010 against India in Ahmedabad.
He has brought metronomic consistency since, with centuries against every country that has played the longest format.
Ahead of the 2015 World Cup, Crowe was asked about Williamson's development.
"We're seeing the dawn of probably our greatest ever batsman."
He chose Williamson over a field of candidates which includes himself, protégé Taylor, Turner and Bert Sutcliffe.
Williamson reached the record century mark in 114 innings across 64 tests; Crowe took 131 innings across 77.
Not that the milestone will matter a jot to the New Zealand captain.
If pedigree is a judge, he will be more concerned in enforcing his side's dominance over England after the visitors were routed for 58 in yesterday's opening session of the first test.
The hosts are 197 for three in reply after starting the day at 175.
Last night Williamson led the way with 91 from 177 balls as he numbed the tourists with patience under the floodlights.
His batting, alongside Tom Latham's stoic 26 off 112 balls, Taylor's 20 and Henry Nicholls' 36 not out took an axeman's grip on the country's maiden day-night test.
Kane Williamson’s century list
1. 131, v India, Ahmedabad, test 1, November 2010
2. 102 not out, v South Africa, Wellington, test 12, March 2012
3. 135, v Sri Lanka, Colombo, test 18, November 2012
4. 114, v Bangladesh, Chittagong, test 26, October 2013
5. 113, v India, Auckland, test 30, February 2014
6. 113, v West Indies, Kingston, test 32, June 2014
7. 161 not out, v West Indies, test 34, Bridgetown, June 2014
8. 192, v Pakistan, Sharjah, test 37, November 2014
9. 242 not out, v Sri Lanka, Wellington, test 39, January 2015
10. 132, v England, London (Lord’s), test 40, May 2015
11. 140, v Australia, Brisbane, test 42, November 2015
12. 166, v Australia, Perth, test 43, November 2015
13. 108 not out, v Sri Lanka, Hamilton, test 46, December 2015
14. 113, v Zimbabwe, Bulawayo, test 50, August 2016
15. 104 not out, v Bangladesh, Wellington, test 57, January 2017
16. 130, v South Africa, Dunedin, test 59, March 2017
17. 176, v South Africa, Hamilton, test 61, March 2017
18. 100 not out, v England, Auckland, test 64, March 2018
