WHITE SULPHUR SPRINGS, West Virginia, July 8, 2012 (AFP) - Potter, ranked 218th in the world, erased a four-shot deficit with five holes remaining in regulation, carding a final-round six-under 64 to join Kelly on 16-under 264.
Kelly, who started the day two shots behind overnight leader Webb Simpson, had five birdies in his four-under 66 on the Old White TPC course.
Simpson, who claimed a first major title with his US Open triumph at The Olympic Club in San Francisco last month, surrendered a one-shot lead on the back nine of the final round here for the second straight year.
Four bogeys in five holes from the 12th spelled the end of his challenge and he closed with a 73 that left him tied for seventh.
South Korea's Charlie Wi and rookie Charlie Beljan shared third place on 14-under 266. Wi posted a 65 and Beljan a 67.
Potter became the second rookie to win on the US tour this season.
After capping his fourth round with an eagle and a birdie, he had a chance to win at the second extra hole -- the 17th that he had eagled in regulation.
After coming up short of the green, Potter chipped on to about five feet but missed the birdie putt as Kelly saved par from a greenside bunker.
Returning to the par-three 18th, Potter landed his tee shot four feet from the pin and made the putt for the victory.
He became the sixth first-time winner on the tour this season. He earned a winner's prize of $1,098,000 and jumped from 173rd to 51st in the FedEx Cup playoff standings.
It was quite a turnaround for the 28-year-old left-hander, who had missed five straight cuts coming into the tournaments.
Kelly still notched his best career finish, improving on a prior tie for 37th.
Leading final-round scores on Sunday in the $6.1 million US PGA Greenbrier Classic (x-won in playoff. USA unless noted, par 70):
264 - x-Ted Potter jnr 69-67-64-64, Troy Kelly 69-67-62-66
266 - Charlie Wi (KOR) 67-66-68-65, Charlie Beljan 70-62-67-67
267 - Daniel Summerhays 68-67-68-64
268 - Martin Flores 64-68-69-67
269 - Roberto Castro 71-64-71-63, Kevin Na 69-67-68-65, Sean O'Hair 66-68-69-66, Ken Duke 66-68-65-70, Webb Simpson 65-66-65-73
270 - John Daly 68-67-70-65, David Hearn (CAN) 69-68-67-66, Jerry Kelly 66-66-70-68, Scott Piercy 66-68-68-68, Graham DeLaet (CAN) 67-70-64-69
271 - Kevin Chappell 69-66-69-67, Davis Love 69-66-68-68, Jeff Overton 70-65-67-69, Carl Pettersson (SWE) 71-65-66-69, Blake Adams 67-70-64-70
271 - Will Claxton 73-65-69-65, Garth Mulroy (RSA) 65-74-67-66, Steve Stricker 69-67-68-68, Jonathan Byrd 64-68-70-70, Steve Wheatcroft 70-68-64-70
273 - Jeff Maggert 64-68-74-67, Rod Pampling (AUS) 69-67-70-67, Pat Perez 71-66-69-67, Gavin Coles (AUS) 68-68-69-68, Seung-Yul Noh (KOR) 68-67-67-71, J.B. Holmes 65-68-66-74, Dustin Johnson 71-67-68-68