The Black Caps have somehow achieved an astonishing victory in the final moments of a test — again.

A fortnight after a one-run win over England that seemed to have supplied enough thrills for a summer, Kane Williamson conquered Sri Lanka on the last ball of another thrilling match at Hagley Oval.

The former skipper, who spent the afternoon compiling an expertly paced unbeaten century, carved a boundary through point to level the scores with two deliveries left.

Williamson then ducked under one bouncer and waved unsuccessfully at a second but scampered through for a match-winning bye and barely beat a throw that, had it dislodged the bails a touch sooner, could have produced an improbable draw.

The masterful innings of 121 guided New Zealand to a target of 285 that represented the third-highest successful chase in this country’s test history.

Coming only a couple of weeks after Neil Wagner bowled the Black Caps to a scarcely believable one-run triumph over England, this two-wicket victory was equally as dramatic.

Williamson’s steady accumulation was initially complemented well by Daryl Mitchell’s aggression, the pair putting together a pivotal fourth-wicket stand of 142 from 157. But when Mitchell and Tom Blundell were removed with half an hour to play, the hosts still needed 46 from 39 with five wickets in hand.

Michael Bracewell’s driven boundary reduced the target to 20 off 18; his wicket a couple of balls later left Sri Lanka looking for four more scalps.

Fifteen runs were required from the last two overs and, after Tim Southee had holed out, eight was the magic number as Matt Henry joined Williamson for the final over.

Henry’s desperation wasn’t enough to avoid a runout, leaving Wagner to charge to the crease in a manner belying the bulging disc in his back and the tear in his hamstring.

Celebrating his 37th birthday, Wagner’s unlikely turn of speed was then called into action for the match-winning run, as Williamson further cemented his status as this country’s greatest batsman.

The 32-year-old’s 26th test ton was integral last month in helping his side sneak back into a second test that England had dominated. No 27 came up in fading light this evening, with 32 still needed, and finding the gaps while tearing between the wickets, that half-finished job was eventually, amazingly, completed.

It initially looked like rain would prove a spoiler in an evenly poised test, the teams unable to take the field until mid-afternoon for a 52-over sprint to the finish.

With New Zealand resuming on 28-1 and requiring 257, at a run rate of a tick under five, the early losses of Tom Latham and Henry Nicholls could have dissuaded the home side from mounting a serious chase.

But playing on a pitch still tricky for batting, a compelling test that had seen control shift back and forth still featured several more swings.

The first came when Williamson’s stay was almost ended on 33, fortunate to see wicketkeeper Niroshan Dickwella spill an edge low to his right.

Nicholls fell the following over but, joining Williamson when the hosts still wanted 195 runs from 34 overs, Mitchell signalled his intentions with a first-ball six.

The asking rate edged above six but Williamson was beginning to target the boundary, bringing up his 50 as the target dropped below 150 with 24 overs remaining.

Sri Lanka were shifting towards defensive mode, and spinner Prabath Jayasuriya ceded three wides in one over with a negative line outside leg.

Heading into the last hour, New Zealand needed 101 more from 90 balls. From such a position, the sun still shining, it felt like there could be only one winner. The third and fourth sixes of Mitchell’s innings made the equation an eminently achievable 78 from 72.

The pressure on the fielders soon brought miscues, New Zealand now collecting singles to seize victory. But there were a couple more complications to come, the first when Mitchell unluckily dragged onto his stumps.

Fifty-three runs were required from eight overs as Blundell joined the drama, and when Fernando yorked the wicketkeeper after only five balls, Sri Lanka had a sniff.

The cheap wickets of Bracewell, Southee and Henry heightened that sense, but Williamson’s despairing dive would soon become the defining image of another breathtaking day of cricket.