Williamson's heroics lead NZ to epic last-ball win over Sri Lanka

The Black Caps have won another Test match off the final ball, with Kane Williamson this time the hero in an epic two-wicket win over Sri Lanka at Hagley Oval this evening.

Needing one to win off the final ball of the game, Williamson and an injured Neil Wagner scampered through for a bye, with the former diving over the line to seal the win despite Sri Lanka getting a direct hit at the non-striker's end.

Williamson finished not out on 121, his 27th Test century, and one of his most important given the context of the game.

Rain in Christchurch on the morning of day five limited the final day to just 52 overs, with New Zealand still requiring 257 for victory with nine wickets in hand.

New Zealand lost Tom Latham early while Williamson first survived a close LBW call before being dropped by Sri Lankan wicketkeeper Niroshan Dickwella.

He and Daryl Mitchell kept the scoreboard ticking over, with Mitchell in particular ramping up the scoring rate.

Mitchell finally fell for 81 with New Zealand needing just 53 for victory at just over a run a ball.

But nobody was able to stay with Williamson, with Tom Blundell (3), Michael Bracewell (10), Tim Southee (1), and Matt Henry (4) all falling, leaving Wagner - injured with a torn hamstring and bulging disc - to partner Williamson for the final three balls.

Needing five to win, Williamson blasted a square drive for four, somehow splitting the two men placed out on the rope.

With one to win off the final two deliveries, Asitha Fernando bowled a bouncer that was close to being called a wide for being over head height, but was not given.

Then the final ball. Another bouncer, a wild slash from Williamson, a charging Wagner diving for the line at the striker's end, and Williamson just touching down at the non-striker's before Fernando threw down the stumps.

It was the Black Caps' second wild finish in as many weeks, after an epic one-run victory over England in Wellington.

Mitchell was awarded man of the match for his scores of 102 and 81 in the Test, and said the Kiwi spirit helped lead the side to victory.

"I think it's something we do pride ourselves on as Kiwis, is that we always try and find our way out of any situation to get stuck in," he told Spark Spot.

"I thought Wags running with a torn hammy and a bulging disc, but also the way Kane played there and managed the innings [showing] what a world-class player and leader he is was pretty special."

New Zealand captain Tim Southee said it was a "great time for Test cricket".

"It's as exciting as it has been for a long time."

The loss for Sri Lanka means their chances of qualifying for the World Test Championship final later this year have now been dashed. The final is now confirmed to be between Australia and India, who incidentally are currently wrapping up a four Test series in India.

Knowing they needed to win in order to keep their hopes of qualifying alive, Sri Lankan captain Dimuth Karunaratne said his side had to go for it.

"The boys tried really hard, unfortunately we were on the losing side, but I think it was a pretty good game.

"It's disappointing for us, but if you look at the positive side I think we've done really, really well compared to the last one. I think the boys have done a really good job this World Test Championship, looking forward to the next one."

The second Test begins in Wellington on Friday.