With plenty of English support in the Caribbean sunshine in Barbados, England had little trouble in surpassing Pakistan's total of 147 with three balls to spare.
Pietersen, who helped Royal Challengers Bangalore reach the semi-finals of IPL 3 scoring two fifties, displayed the touch that once established him as the most exciting batsman.
His 73 from 52 balls, including eight fours and two sixes, steered England home comfortably.
Pakistan got off to a bright start, putting up 50 inside seven overs, but their momentum was lost after the introduction of spin and Graeme Swann claiming the vital wicket of opener Salman Butt, who scored 34 off 26 balls.
Slow left-armer Michael Yardy took two wickets, but the second major breakthrough wicket came when Pietersen made a superb running catch in the deep to get rid of Umar Akmal, who had scored 30 off 25 balls.
Pakistan's troubles were partially self-inflicted, skipper Shahid Afridi getting himself out attempting a suicidal run from his first ball.
England's South African-born opening pair of Michael Lumb and Craig Kieswetter put on 44 for the first wicket before Lumb went in the sixth over.
England were helped by poor fielding from Pakistan who dropped five catches, three by Saeed Ajmal.