On a sluggish, low-scoring Lord's pitch that allowed ball to dominate bat in a manner that would have had the England and Wales Cricket Board's marketing department in a cold sweat, Gregory conjured a box office finish for the showcase.
Chasing what had looked a slender target of 121, Gregory faced up with the score at 110 for eight and needing 11 to win from the final set of five from Richard Gleeson.
He launched the first of those riotously over mid-wicket for six - just the fourth maximum of the day, in a format designed to encourage big hitters - before flicking the subsequent full toss for four to effectively settle matters in the Nottingham side's favour.
Gregory lashed the next ball through the covers before leaping into the air, finishing up a two-wicket win with two balls to spare.
In a match that saw a top score of 26 and included 74 dot balls, his 17 not out from six balls was a game-changer of a knock when the pressure was peaking. Sam Cook, who claimed four for 18, was the pick of the bowlers in helpful conditions.
With a modest target on the board, a place in England's T20 World Cup squad waiting to be filled following Jonny Bairstow's injury and Phil Salt failing to seize his moment in the first innings, the stage had earlier seemed set for an Alex Hales special.
One trademark 'Hales storm' would have cranked up the volume around the end of his three-year stint in the international wilderness, but he was unable to oblige.
He mustered nothing more emphatic than a run-a-ball eight before throwing his hands at an angled delivery from Ireland's Josh Little and skying a catch to cover. Instead, the tournament's leading run-scorer, Dawid Malan, assumed responsibility.
On the occasion of his 35th birthday, he seemed intent on making it a double celebration. But while he was in the middle for just under half the innings, he was a reassuring presence that never quite left his mark.
Any hopes Malan had of playing the anchor role ended when Paul Walter held one up in the pitch and drew the gentlest of leading edges. By then Matt Parkinson had already prised out Tom Kohler-Cadmore lbw and it was clear the battle was on.
Colin Munro showed he had the muscle to end things in a hurry, launching a six and two fours in a hurry, but could not match it with durability, holing out to Parkinson with 53 still needed. By the time Samit Patel joined him, the Rockets needed another 35 from the final 25 deliveries.
Ordinarily that would not be daunting but in these conditions it looked to be too much until Gregory's late show.
The Originals kicked their innings of 120 for nine off with a hapless powerplay, a couple of quick-fire boundaries from Salt proving a red herring as they meandered towards a score of 23 for three.
Cook set things off by pinning captain Laurie Evans lbw in his opening set, then sent Wayne Madsen's stumps flying as an attempted scoop backfired emphatically.
By the time Salt added to his side's woes, mis-timing one horribly and chipping Daniel Sams to mid-on, there was already a mountain to climb. Between them, and in spite of some chaotic running, Ashton Turner (26) and Tristan Stubbs began to make a fist of it.
Turner released some of the building pressure by swatting Patel for six, while both players got after Lewis Gregory. Their 35-run stand was just beginning to find its legs when the canny Patel swiped them.
He found himself on a hat-trick when Stubbs top-edged a swipe across the line and picked up the in-form Walter for a golden duck.
He was unable to make it three in three but circled back for Turner, whose fluent knock was cut short courtesy of a slog sweep that came up short.
Tom Lammonby dragged the total up past three figures with a busy 21 but when Cook picked up where he left off, yorking the Somerset man and tailender Gleeson, it was enough to set the scene for the Rockets' late charge.