Lancashire 296 for 8 (Buttler 91, Croft 67, Guptill 50, Rankin 4-66) beat Warwickshire 254 for 9 (Bell 73, Trott 66, Parry 3-43, Smith 3-45) by 42 runs
Buttler hit a typically creative 91 off 73 balls to underpin the Lightning's 296 for 8, which also included half-centuries for Martin Guptill (50) and captain Steven Croft.
Left-arm spinner Parry, who has also played alongside Buttler in England's one-day team since the last Royal London Cup campaign, then put the squeeze on the chase with an excellent 3 for 43 from ten overs as Warwickshire finished with 254 for 9.
Warwickshire captain Ian Bell said: "It was an outstanding toss to win. We definitely wanted to bat first, and we saw that it got harder and harder as the game went on.
"I think Jos Buttler was the difference in the way he played. He showed the options you need to turn a par score into one above par. Without him in the side, they'd have probably only got 260, which we would have been very confident in chasing. To all our young players watching that, they can learn a lot from the shots he used, the angles he created and the calmness he had."
Bell was part of a third-wicket stand with Jonathan Trott which had put their side on course to reach 297.
But wily Parry, in particular, and seamer Nathan Buck turned the screw with some tight bowling. Trott, who passed 9,000 List A runs in the process, posted 66 and Bell went on to make 73.
Parry had Trott superbly caught at cover by Croft before later getting Laurie Evans in identical fashion. He had also got Will Porterfield caught at mid-wicket by the same man for 40, with each of Croft's three catches all diving efforts. In the final reckoning, Croft actually finished with four catches.
From the start of the 33rd over to the end of the 42nd, Warwickshire had slipped from 163 for 2 to 198 for 5, with Jordan Clark also bowling Tim Ambrose. When he departed, the equation was an unlikely 100 off 51 balls.
But the innings of the day belonged to Buttler, who hit ten fours and a six.
Remarkably, it was Buttler's List A debut for Lancashire despite joining from Somerset ahead of 2014 - and it was his highest score for the county in both forms of limited overs cricket.
Buttler and Croft - 67 off 70 - shared 122 inside 19 overs for Lancashire's fifth wicket to advance from 118 for 4 after 24 overs, and it was a fifth-wicket record stand for the Lightning against Warwickshire. Both men hit a six, straight in Buttler's case and over long-on for Croft. Buttler was typically inventive, scooping Rankin for successive boundaries at one stage.
Buck later got Bell caught and bowled off a top-edge at the start of the 48th over as he attempted to cut loose with Warwickshire needing 57 off the last three.
Lancashire, including four players making their List A debuts for the county, bowled extremely well. One of those debutants, Buck, finished with 2 for 53 from ten. Tom Smith also returned 3 for 45 from eight, including two wickets in the last over.