Mystery has ruled spin bowling in the Twenty20 age. Short-format slow bowlers are no longer measured by how far they can spin the ball, but in how many directions. As the Sunil Narines and Saeed Ajmals of the world leave batsmen groping open-mouthed in their wake, the likes of Ravichandran Ashwin wonder if they are not being too square. Orthodoxy still works, but this new stuff is dynamite.
To label Rangana Herath a throwback to cricket's black-and-white days would be glib. He was, after all, the modern progenitor of the carrom ball, even if his prototype version of the delivery would never compete with the sleek new models. There is, of course, a charming devotion to tradition in Herath's method; he is a zealous disciple of flight, a long-time servant of dip and spin. But to say there is more to Herath than meets the eye would not just be an ironic comment on his figure. The enigma of his success is as emphatic as the unknowns that shroud any doosra or flipper.
As Herath slammed the opposition top order into the turf in Chittagong, New Zealand's batsmen committed to more wrong lines than a drunk at a karaoke bar. The pitch took more turn than it had all tournament, but it was hardly spitting square. Slow bowlers would almost certainly have had more value for their revs up north in Mirpur, yet, there New Zealand's batsmen were, feeling for the ball, prodding like they could not pick the man who only spun it in one direction all night.
After the match, Herath was telling television presenters there was nothing more to his haul than "bowled the ball in the right place". It is the reply he always gives, but 217 Test wickets in, does anybody still believe it? Five wickets for three runs are not figures befitting a bowler who simply put the ball on a length. Positive batsmen, drenched in form, do not stall and scatter at the sight of such uninspiring diligence.
So what gives? In Tests, Herath's prey is lured gently. He bowls one from out wide, another in front of the stumps, flighting the first, darting the second, adding threads as he goes, before the batsman is strung up, suddenly, dead in the web. He cannot build an insidious narrative in four T20 overs, but in Chittagong, he had condensed that mode of attack, and therein found the means to make fools of New Zealand's two most experienced batsmen.
He flighted one up to Brendon McCullum's off stump to show him the appreciable turn first, then angled a slower one on the pads. McCullum dared not hit against the spin so early, especially if Herath had ripped it in. Another flighted, turning ball on off stump, then a dart - the first one - on the pads. The ensuing appeal was correctly turned down, but having delivered four dot balls now, Herath knew McCullum's next move long before the batsman made it. He floated one up wide of the stumps, as McCullum charged out. The ball dived and turned to beat the blade.
Ross Taylor, arguably the better player of spin, was outmanoeuvred even more forcefully. From the first two balls, Herath determined Taylor could not pick which one would turn and which would slide on, so he alternated between them, raising two appeals in the first four balls, before nailing him with the fifth. Herath was a step ahead as he beat both batsmen, first in the mind, then off the surface. That he is accurate and artful is plain, but as batsmen trudge off, they know he is good, but few understand exactly why or how. New Zealand's top order have known the feeling before.
"In the past Rangana aiya had dismissed their top order batsmen," Lasith Malinga said after the match. "Brendon McCullum and Ross Taylor struggle against him. I had hoped to get him into the attack as soon as possible. He was successful and my decision was too."
Malinga may simply have been committing to the ruse with that statement, for although he is the captain on the team sheet, he was not the man who set Herath's fields. Mahela Jayawardene had Sri Lanka's reins, and no matter who walks out for the toss on Thursday, they would be wise not to relieve him of them.
So often the flagbearers for fight in global events, New Zealand encountered a man whose fire consumed their own in Chittagong. Sri Lanka had made each of the last five semi finals in global events, and with one of the great T20 spells, Herath ensured hope for that elusive title would not wither just yet.

Andrew Fidel Fernando is ESPNcricinfo's Sri Lanka correspondent. He tweets here