South Africa-born Pietersen, ranked Sunday as the world's second-best one-day batsman behind Australia captain Ricky Ponting, failed to make much of an impression during the three-match series.
And on Saturday he was out for a second-ball nought in Nottingham during West Indies' 93-run win which gave the tourists a 2-1 victory overall.
Powell produced a classic piece of fast bowling, softening up Hampshire shotmaker Pietersen with a first-ball bouncer before having him caught in the slips with a full-length delivery.
"After the first Test at Lord's (where Pietersen made a hundred), we realised that if we attacked him, he tried to go out of his shell and it progressively worked for us in the one-day series. We attacked him a lot and it paid off for us," Powell explained.
"To me, he's the kind of person who doesn't like people to get on top of him. When he comes out to bat, I normally talk to him and stuff like that, tell him things that probably make him uncomfortable.
"This time I didn't do that. I bowled a sharp ball at him and give him a stare. Then I got my ball in the right area, he went and played a stroke and he nicked one."
Powell added he had tried to learn from some of the world's leading fast bowlers. "When you watch (South Africa's) Makhaya Ntini and Shaun Pollock, they just give a batsman a stare and the (Australia) great Glenn McGrath did the same thing. I just tried that and it worked."
The 29-year-old Jamaica quick put England, chasing 290 to win, even further on the backfoot by dismissing openers Matt Prior and Alastair Cook in an aggressive opening spell that saw the hosts slump to 33 for three.
Powell, named man-of-the-match after finishing with four wickets for 40 runs added: "For the past couple of seasons representing the West Indies, when it's come to crucial games like this I haven't picked up any wickets at all, even in the last game of the World Cup (where England beat West Indies in Barbados).
"On Friday night I sat in my hotel room and thought about what I had to do to create pressure and take early wickets.
"On Saturday morning, I assessed the wicket when our guys went out to bat and I realised I had to bowl straight and vary my pace. I thought about my game, and put the ball in the right areas."
Powell, who has previously expressed a desire to play county cricket, also revealed he'd been in talks with Welsh side Glamorgan.
"I'm still in negotiations. It would be nice to play some county cricket here whether it's Glamorgan or whoever.
"Playing county cricket, would help my game improve a notch for West Indies cricket as well. I just want to use it to propel my game to the next level."