England chased down South Africa's daunting 222/6 with five balls to spare to register their second-highest successful run-chase in the format. Morgan, who led the show with an unbeaten 57 off 22, said the win reinforced his side's belief that they could hunt down any total with their authoritative approach.
"It creates belief that you can chase down anything, and it reinforces what our method is in chasing big totals down," said Morgan. "It's a reference point to what we can do, there's no limit on restricting yourself to certain things.
"You want to leave everything out there with the bat. It won't always work, but it will give us the best chance of winning. Moving forward from this series, our learning will continue to get better, hopefully, because I don't think we've played at our best in this series."
Morgan praised Jos Buttler and Jonny Bairstow for their 91-run stand for the second wicket, which laid the foundation for the chase, and pointed to their counter-attacking approach against left-arm wrist-spinner Tabraiz Shamsi as one of the decisive junctures in the chase.
"There are a couple of key match-ups when you're looking at chasing down scores like that that give the side belief," he said. "[Shamsi was] one of their key bowlers throughout this series, and today would have been [key], and to take on a guy like that in the way Jonny and Jos did, [it] reinforces how good the wicket is and how good those guys are at the crease.
"That creates a lot of belief in the dugout and the changing room that we're not standing back, we're moving forward and trying to get better. If we can continue to do that at key points in the game, then we'll become a better side."
One of the positives for England was the performance of Buttler, who put behind his failures in the first two games with a breezy 29-ball 57. Morgan restated that the wicket-keeper batsman would continue to bat at the top in T20Is, and compared his ball-striking skills to those of former South Africa star AB de Villiers.
Buttler is one of our greatest-ever white-ball cricketers. I think he has as much talent as someone like AB de Villiers.
"If he'd failed today, he still would have been considered in the top three," Morgan said. "He's a very fine player. He's got unbelievable ability to take any bowling line-up apart, and to have somebody in your side like that is great.
"He is one of our greatest-ever white-ball cricketers," Morgan told Sky Sports. "I realise why people talk about him so much, but not in a negative way. I think he has as much talent as someone like AB de Villiers."