After calmly eclipsing the world record sixth wicket partnership in a 365 run knock with Blackcap teammate BJ Watling, Tauranga's Kane Williamson summed it up with 'we just needed to bat as long as we did”.

Yesterday the two Northern Districts batsmen put the Blackcaps in control of the second test with Sri Lanka at Wellington's Basin Reserve, with the pair's record stand passing the old mark of 352 set by Watling and New Zealand captain Brendon McCullum on the same ground last February.

The 24-year-old's double-century (242 not out) and a ton from BJ Watling (142 not out) saw the Blackcaps pile on a world-record 365 runs for the sixth wicket, before finally declaring at 524-5.

Williamson, who batted 10hr 23min and faced 438 balls, notched up his first Test double century, while Watling - eight hours and 333 balls faced – also ended with a career high test score.

Speaking to media after stumps on day four, Williamson says having been under pressure at 159-5, a mere lead of 24, the thought at the front of the duos minds was to try and bat the home side back into the contest.

The 24-year-old carefully went about finding the balance needed between time and runs, and was content with marking the crease before capitalising on the odd loose delivery.

Kane says: 'You just have the team as your main focus and it keeps you going, and I think that's very much what BJ and I were thinking about.

'That was important because we needed to draw on that to bat as long as we did.

'That was very much the motivating factor. You talk about 100s or 200s - it's great to get them but it's more important to keep going to put the team in a better position.”

Williamson knows he did have some luck. He was dropped twice on Monday and at 104 wicketkeeper Prasanna Jayawardene put him down off spin bowler Rangana Herath.

Then on 233, Jayawardene badly missed a stumping off Herath when Williamson was stranded down the pitch.

When McCullum finally declared and the pair walked off Sri Lanka had an imposing target of 390 to win and went to stumps at 45-1 – still 345 from an unlikely victory.

Having been at the crease for such a period, Williamson admits that sometimes it is a challenge to remain mentally focussed and put the team first.

Yet looking back at the innings he is content.

'Obviously it was great to do what we did,” he adds. 'For BJ to play so well and for both of us to put together a big partnership.

'I suppose it wasn't without a bit of luck on a very good batting wicket which we know we are going to work hard [today] to take nine more wickets.”

It was Williamson's ninth test century. Only Martin Crowe (17), John Wright and Ross Taylor (12), and Brendon McCullum and Nathan Astle (11) have scored more for New Zealand. It is the seventh-highest score by a New Zealand batsman in a test.

He passed 3000 test runs at 208, becoming the fastest New Zealand batsman to the mark - in 71 innings.

The Blackcaps have since gone on to clinch the series 2-0, bowling Sri Lanka out for 196 this afternoon, winning by a margin of 193 runs.