The Lions, needing 132 runs to win, started their chase conservatively before Alviro Petersen and Gulam Bodi got stuck into Iain Wardlaw in the third over with three boundaries.
Petersen was dismissed by T20 debutant Oliver Hannon-Dalby in the fourth over for 19 runs, and Bodi soon followed, trapped leg before by Steven Patterson for eight as the Lions chase tottered at 31/2 after five overs.
Quinton de Kock and Neil McKenzie went about rebuilding the Lions innings, posting 38 for the third wicket, with De Kock hitting a couple of sixes while McKenzie found the gaps to keep the scoreboard ticking over.
Azeem Rafiq, who took 1/14 from four overs, removed McKenzie for 13 in the tenth over.
Yorkshire then kept the Lions tied down, with the pressure resulting in De Kock top edging Wardlaw into the air to be caught for 32.
Tight bowling swung the innings Yorkshire’s way, as Jean Symes struggled, with the Lions needing 41 runs off the last five overs.
Dwaine Pretorius relived the pressure with 14 runs off Adil Rashid in the 16th over, with the Lions bringing up their ton.
However, Pretorius was out in the next over for 25, caught in the deep off Patterson as the game moved towards a tense finish.
Symes and Thami Tsolekile were held off by disciplined bowling from Patterson and Wardlaw until Symes hit Hannon-Dalby for six and four in the penultimate over to turn the game in the Lions' favour.
Symes wrapped it up in the final over, as they reached 134/5 to secure victory with four balls to spare, smashing Patterson down the ground for four.
The match had started in overcast conditions as the Lions bowlers managed to restrict Yorkshire's opening pair of Phil Jaques and skipper Andrew Gale after the home side won the toss and chose to bowl.
Yorkshire scored at about a run-a-ball in the early stages, reaching their 50 without loss after Lions skipper Petersen introduced himself for his first bowl of the tournament in the seventh over.
Pretorius replaced spinner Aaron Phangiso and immediately produced the wicket of Gale for 21, caught behind by Tsolekile.
Phangiso then had new batsman Joe Root caught on the boundary by Sohail Tanvir for five for his seventh wicket of the tournament.
After a brief rain interruption midway through the innings, Petersen bowled Jaques for 31.
Yorkshire then stepped up the scoring before Phangiso had Gary Ballance caught for 18 by Dirk Nannes. The left-armer finished with figures of 2/23.
Adam Lyth, after hitting Yorkshire’s first six, departed in the 18th over, caught by Nannes off Chris Morris for 21.
Yorkshire’s late innings charge was stifled as they lost regular wickets, eventually reaching 131/7.