'We have a bowling group that is world class and can take take 20 wickets'

While impressed by Kane Williamson's match-winning century, New Zealand captain Brendon McCullum praised his bowlers for their tenacity and ability to change plans to suit the conditions, which helped them seal a series win over Sri Lanka.

Williamson's 108 not out guided the hosts to a five-wicket victory before lunch on the fourth day of the second Test in Hamilton on Monday, earning him the man-of-the match award.

The win also ensured New Zealand swept the two-test series against Angelo Mathews' side, following a 122-run first Test victory on the benign pitch at University Oval in Dunedin.

Neither side were truly comfortable in the second match at Seddon Park, with the pitch providing more pace and steep bounce than expected without producing much swing or seam movement.

"It was bizarre," McCullum said in a televised interview. "Plans changed during the Test match.

"The short-pitched bowling became a real weapon on a wicket that had plenty of pace and bounce on it.

"At times you see some of the shots that don't look that good, but then you think of the constant pressure that has built up by both teams ... and it brings those sorts of mistakes.

"It takes a very special player to overcome those and we saw that in Kane."

New Zealand's bowlers, who struggled in the first Test against Australia in Brisbane last month before finding form in the inaugural day-night Test in Adelaide, kept plugging away on a flat Dunedin pitch before eventually getting their reward.

Sri Lanka did not make it easy for them, lasting 117 overs in scoring 294 in their first innings and then 95 overs in the second to make 282.

"The guys have got better as the season has gone on," McCullum said of his bowlers. "In Australia we were a little bit short of a gallop in terms of where we wanted to be and where we operate.

"But what we are seeing is a team that is continually improving and a bowling group that is world class.

"We know we have the ability to take 20 wickets when we're on song, it's just a matter of making sure we're working together in partnerships and trying to build as much pressure as we can, because we know we have the ability to bowl those wicket-taking balls."