A brilliant seven under par 65 took Poulter from four behind to a two-shot victory - and a $1.2m (Dh4.4m) cheque at Mission Hills.
The 36-year-old, winner of all his four games in Europe's amazing cup triumph five weeks ago, had eight birdies in the first 15 holes and led by three at that point.
A bogey on the short 17th was followed by a second shot into sand down the last, but he made a nine-foot putt for par and it was all over when Phil Mickelson failed to hole his approach on the difficult 18th.
That left the two-time winner in a four-way tie for second on 19 under par with fellow Americans Jason Dufner and Scott Piercy and also current Open champion Ernie Els.
Lee Westwood led by three early on, but double-bogeyed the short fifth and had three back nine bogeys.
He finished in a tie for sixth with South African Louis Oosthuizen, the two overnight leaders both disappointing with closing 72s.
Meanwhile, organisers of the completion confirmed it will return to Shanghai next year with an increased, Major-size $8.5 million prize purse.
The event will also be included as an official event on next year's PGA Tour schedule, with the winner earning a three-year exemption to play on the American circuit.
"Today's announcements are important in elevating the status of the WGC-HSBC Champions as a whole," said PGA Tour commissioner Tim Finchem.
The tournament, likely to be Asia's richest next year, was played at Shanghai's Sheshan course for its first seven editions before moving temporarily to Mission Hills, near the Hong Kong border, this season.