Griffin, a self-described son of hippies who was named after a spiritual master, shed tears of happiness upon sinking a six-foot par putt to clinch his breakthrough victory at the Golf Club of Houston.

"I felt eerily calm. I don't know why," he said in a greenside interview after carding three-under-par 69 to edge fellow Americans Scott Harrington and Mark Hubbard by one stroke.

Griffin, 31, is no spring chicken but was making only his 33rd start on the PGA Tour.

He finished at 14-under 274 and now leads the early FedEx Cup points list. Apart from confirming his place at next year's Masters, he also has the job security that comes with a two-year exemption.

"I just knew if I make bogey I have a job out here next year," he said of the final hole, where his first putt from 60 feet drifted well beyond the cup, leaving a testing one coming back for the win.

"I'm just so relieved it's over. I played really solid. I'm so proud of the way I hung in there.

"Putter let me down a little bit on the back nine but my iron shots were pretty darn good. It's pretty surreal."

Griffin was born in California but grew up in Virginia, of modest financial means.

Raised a strict vegetarian, he took up golf at age eight, and subsequently threw himself into the game after his father was diagnosed with an ultimately fatal brain tumour.

Griffin's mother is still alive and he promised to buy her a new car if he won on Sunday.

With prize money of $1,350,000 ($A1.99 million) it should not be a problem.

Rhein Gibson, the only Australian to make the cut, carded a six-over 78 on Sunday to finish the week at eight over.

Americans dominated the event with China's Xinjun Zhang (66), Mexican Carlos Ortiz and Austrian Sepp Straka (both 69s) the only overseas golfers in the top 20 - in a five-way share of fourth at 11 under.

Australian Associated Press