The 33-year-old banked a cheque for one million US Dollars (£768,409) after a four-under round of 68 took him to 17 under for the week.
Aside from his part in Europe's historic Ryder Cup success, 2012 has not been a halcyon year for McDowell and he admitted yesterday's win was a big morale boost.
"This really caps off my season," McDowell said.
"We try not to put winning on a pedestal, but this one feels very sweet because it's been a grind all year.
"Certainly I will draw some confidence from this one. The game hasn't given me a huge amount this year."
McDowell started the final day two shots ahead of Keegan Bradley and ensured success with a strong back nine.
He was one under at the turn, having picked up a stroke at the par-five second, but strengthened his case on the back nine with four more birdies to balance against a solitary bogey-six at the 13th.
Bradley started strongly, with birdies at holes two and five but was level-par for the front nine after giving back shots on eight and nine.
He finished three under for the round as he responded to McDowell's surge but it was not enough.
The pair were well ahead of the rest of the 18-man field, Bo Van Pelt finishing third four shots back from Bradley and seven adrift of McDowell.
Tournament host Tiger Woods finished in a share of fourth alongside Rickie Fowler and Jim Furyk on nine-under.
Zach Johnson spared England's Ian Poulter last place with a dreadful round of seven-over that included three double bogeys and three bogeys.