Simpson, whose only prior PGA title came two weeks ago at Greensboro, birdied his last three holes to take the crown, dropping a 26-footer at the 18th in regulation and a 15-footer on 18 in the playoff to set up the winner.
“It was great,” Simpson said. “To finish the way I did, birdies on 18 and then birdie 17, it was awesome.
“I thought winning the second time would be easier but it wasn’t.”
Reavie, whose only PGA title came at the 2008 Canadian Open, could only wonder what might have been after taking a bogey on the final regulation hole to fall into the playoff.
Simpson and Reavie each finished 72 holes on 15-under par 269 after Simpson sank his long birdie putt on the par-5 18th to finish a round of 65 and then watched as Reavie botched his chance to win in regulation.
Reavie laid up short of the 18th green and lofted his sand wedge approach over the green. He missed a 12-foot putt for his first bogey in 30 holes to finish on 66 and fall into the playoff.
“Unfortunately, my wedge didn’t quite work out,” Reavie said. “I’m going to make a 5 there nine times out of 10. But all in all on the day, I played fantastic.”
On the first extra hole, a replay of 18, both players blasted out of greenside rough and sank birdie putts, Simpson’s a pressure-packed 15-footer and Reavie’s from three feet, to continue the playoff.
The second playoff hole, the 17th, saw Reavie miss a 23-foot birdie putt to set the stage for Simpson’s winning putt.
Simpson won the $1.44 million top prize from the $8 million event, the second tournament of the US PGA season-ending playoff series, and seized the overall playoff points lead.
The top 70 players in points advanced to the BMW Championship in two weeks at Cog Hill near Chicago, where only the top 30 in points will qualify for the season-ending Tour Championship the following week in Atlanta.
World No. 1 Luke Donald of England shared third on 271, two strokes adrift, with Masters co-runner-up Jason Day of Australia and American Brandt Snedeker.
US veteran Jim Furyk was sixth on 272, one stroke ahead of countryman Bo Van Pelt with Masters co-runner-up Adam Scott of Australia and American Hunter Mahan on 274.
Donald and Simpson made the turn deadlocked for the lead at 15-under. Simpson birdied the second and Donald the third and then each man birdied the fourth and fifth, eagled the par-5 seventh and birdied the ninth.
After Simpson made a bogey at 10 to fall back, Donald surrendered the lead with a double bogey at the par-4 12th, blasting over the green from a bad lie in greenside rough on his fourth shot.
Simpson joined Scott, Snedeker, Donald and Watson in holding sole possession of the lead, but would not make another birdie until his clutch putt at the 18th to conclude his round.
“It just fell in the side,” Simpson said. “It was fun to make.”
Reavie made his charge late. He birdied the par-3 11th, the par-4 13th and 14th and the par-3 16th to put himself alone atop the leaderboard until his stumble on 18.
“I thought if I could shoot 5- or 6-under I would be right there,” Simpson said. “Chez has just played extrordinary golf on the back side.”
Reavie, who began the season on a medical exemption after knee surgery last year, clinched a Tour Championship spot and berths in three 2012 majors.
“It’s unbelievable,” Reavie said.
Ernie Els, who barely made the 100-man cut for this week at 99 in points, sank a six-foot birdie putt at the last hole to crack the top 70 and keep the three-time major champion from South Africa in the season playoff title hunt.
“When I got to the green, up there on the board I saw I was 71st. I knew I had to make it,” Els said. “In a way it’s good for me. It brings out a little fight in me again.
“I’ve been struggling all year, especially with the putter. I’ve gone to the belly putter. The putts I’ve made will help me in the future. I’m a little more steady than I’ve been. I’ve made some clutch putts.
“Hopefully I’ll play better in Chicago.”