McDowell was three over par for the day in trying weather conditions to finish three under overall, two ahead of a chasing pack of three.
Northern Irishman Gareth Maybin, the unfortunate Damien McGrane of Ireland and Dane Soren Kjeldsen were the only other men to finish under par for the tournament, each closing one under.
McGrane, in particular, will feel aggrieved after losing his composure on the final three holes, during which he dropped four shots.
McDowell's win not only made new inroads into Martin Kaymer's sizeable Race to Dubai lead but also books his place as world No 10 – becoming the sixth European in that group alongside four Americans.
He started the final round as joint leader with compatriot Maybin on six under but both men lost strokes early on to open the way for McGrane, Maybin bogeying his first three holes on his way to a five-over round of 76.
Ireland's McGrane, playing in the group ahead of McDowell and Maybin, started on two under and gradually chipped away to five under to be in the lead on the 16th tee.
But with a second tour win in his sights and heavy wind affecting all the players, he made a mess of the hole and surrendered the initiative.
McGrane sent his tee-shot into the rough on the right and then took on an overly-ambitious shot that backfired before narrowly avoiding going out of bounds.
In the end he needed four shots to reach the green and two putts for a double-bogey six.
McDowell bogeyed the third and eighth before pulling a shot back on the par-four ninth. The US Open champion dropped a further shot in taking four strokes on the 12th but a steady return of pars in the increasingly difficult conditions was enough to ease him into a two-shot lead.
The 31-year-old bogeyed the 18th but still secured his seventh career win.
Jose Maria Olazabal was one of only three players to sign for a sub-par round, with his one-under 70 enough to earn him a share of 10th.
Ben Crane held off Brian Davies to win the CIMB Asia Pacific Classic by one stroke.
Crane held his nerve to hole an eight-foot putt on the 18th at Mines Resort and Golf Club in Kuala Lumpur and sign for a two-under 69 to finish 18 under.