Blackcaps star Williamson, liberated from the burden of red-ball captaincy, struck a classy 200 not out to put his team in control of the opening test against Pakistan on Thursday.
Williamson relinquished test captaincy earlier this month but proved he remains New Zealand's batting mainstay steering them to a mammoth 612/9 before skipper Tim Southee declared with a lead of 174.
Pakistan finished day four on 77/2, still 97 behind and needing to bat out of their skin to deny New Zealand a 1-0 lead in the two-test series.
Opener Imam-ul-Haq was batting on 45 at stumps with nightwatchman Nauman Ali on four at the other end.
Pakistan bowlers had to break their back for the occasional success on a flat track at the National Stadium and more toil awaited them after New Zealand resumed on 440/6.
Overnight batsmen Williamson and Ish Sodhi, who made a career-best 65, combined in a seven-wicket partnership of 159 to frustrate the hosts.
Abrar Ahmed (5/205) finally broke the stand when he removed Sodhi to spark off a lower-order collapse, but Williamson could not be denied his milestone.
With number 11 Ajaj Patel at the other end, Williamson hit Abrar for a six to inch closer to the double hundred and, four overs later, reached the milestone with a single off the spinner.
Williamson, who hit 21 fours in his patient 395-ball knock, removed his helmet and raised his bat in a characteristically low-key celebration and New Zealand declared immediately.
Pakistan's attack looked exhausted having to bowl nearly 195 overs on an unresponsive track.
Spinners Abrar and Nauman (3/185) slogged collectively for nearly 131 overs and the bowlers' task was made tougher by the overall sloppiness of the side.
The hosts dropped three catches, missed a couple of stumpings and twice opted against reviews which would have resulted in wickets.
Pakistan could not escape the final session unharmed either when they came out to bat for the second time in the match.
Abdullah Shafique stepped out against Michael Bracewell only to chip him to the mid-on fielder and Shan Masood was trapped LBW by Sodhi.
Reuters.
