Considering Underhill is an openside flanker, renowned for his defensive quality, and Beauden Barrett is the sport’s silkiest fly-half, he had no right to turn his opponent inside and out before accelerating over into the corner from 20m out.
He did, though, only to see the 76th-minute effort ruled out following the dubious intervention of the TMO Marius Jonker.
England, who had led 15-0 until the final flurries of the first half, trailed the world champions 16-15 at this point on Saturday, in an absorbing Test match worthy of the four-year wait for these giants to finally meet again.
Courtney Lawes had charged down TJ Perenara’s box-kick to gift the Bath flanker his chance at rugby immortality but, after referee Jerome Garces had initially awarded the try, Jonker advised a closer look and duly deemed Lawes was offside.
Replays still left opinion divided. Still, having won by a solitary point against South Africa the previous week when another contentious late decision erroneously went in their favour, England perhaps could have little complaint.
For his part, Underhill was able to remain at ease with it all, despite being denied what would have been a remarkable way to score his first international try in his seventh Test appearance.
“I can’t say I got to think about that (turning Barrett inside out) too much while it was happening, but I was pretty happy to get over in the corner,” recalled the 22-year-old, who, in for the injured Tom Curry, was England’s finest player with some brutal defence and quality ball-carrying.
“It’s a bit of a blur. The ball popped up and I was in the right place.
“I just tried to get the ball in the right hand and go for the corner.
“It was what it was, the decision that was made. It was disappointing.
“It’s tough to take but it was marginal and that’s the game.
“In the grand scheme of things, in terms of the game, there were quite a lot of fine margins like that that could have gone either way and we came out on the wrong end of that and that’s the way it goes.”
Underhill, who took his chance after being ruled out of last two Six Nations games and summer tour of South Africa, conceded he did not even watch replays of the ruck on the big screens as the decision was deliberated.
“When something like that happens, ultimately the ref’s decision is final – if he says the grass is pink then the grass is pink,” he said.
“So we try to refocus for the next job because that’s what’s important; we can’t go back and change anything.”
He is right to say there were other points of fine margins, too; beforehand, England twice kicked to the corner only to see their lineout crucially malfunction while in the closing stages they somehow failed to get into position for a drop-goal attempt.
Hooker Jamie George came on for Dylan Hartley at half-time – the co-captain was nursing a thumb injury – and saw three of his throws go astray and he also conceded a penalty for a dummied dart.
All of that was in stark contrast to the first half when England were supreme.
Indeed, any newcomer to the sport would have presumed they – not New Zealand – were the revered world champions given the manner in which they clinically took control.
Chris Ashton took just 115 seconds to score on his first Red Rose start in four years, the England winger using the wet conditions to slide over when Ben Youngs’s brilliant pass caught the All Blacks dozing on the blindside.
Eddie Jones’s side played with such confidence, attacking with pace and accuracy, and leaving their opponents befuddled.
Owen Farrell swiftly dropped a goal and, with New Zealand cheaply kicking away their possession, his side grew further in belief.
Hartley added their second try in the 24th minute after a quality driving maul from 15m out, backs Farrell, Ben Te’o and Henry Slade all joining in to leave the All Blacks pack in a mess.
Maro Itoje proved immense in that set-piece and, with Farrell improving, everything was so sharp and crisp.
Steve Hansen’s side did not get to grips with them until the latter stages of the first half when Damian McKenzie, outstanding at full-back, crossed and Barrett converted before adding a stoppage-time penalty.
At 15-10, the contest had a different look altogether at half-time but, still, the All Blacks could only forge ahead via the boot of Barrett in the second period and England had those chances.
“We’re gutted but in the week coming up we’ll probably be able to take some heart out of what we did in the game; we will be able to take away a lot from that,” admitted Underhill.