PALM HARBOR, 15 Mar 2015 (AFP) - The 21-year-old American rolled a tension-packed putt over a ridge and into the cup at the par-3 17th on Innisbrook resort's Copperhead course to defeat compatriots Patrick Reed and Sean O'Hair and take the $1.062 million top prize.
"I guess it was just my day," Spieth said.
Spieth, who shared second at last year's Masters, will jump to a career-best sixth in Monday's world rankings and will be among the favorites at next month's Masters, where top-ranked Rory McIlroy will try to complete a career Grand Slam by winning the green jacket for a third consecutive major triumph.
It was the third victory in five months for Spieth even though his only other US PGA victory came in a playoff at the 2013 John Deere Classic. Spieth took the Australian Open crown in November and the Hero World Challenge hosted by Tiger Woods last December.
Reed, Spieth and O'Hair each finished 72 holes on 10-under par 274, one stroke ahead of Sweden's third-ranked Henrik Stenson. American Ryan Moore, the 54-hole leader ahead by three with six holes to play, made bogeys on three of them and finished two shots adrift.
The playoff began at the par-4 18th hole and Spieth missed a 10-foot birdie putt for the victory while Reed, who made a 31-foot birdie putt on the hole in regulation, needed an eight-foot par save to stay in the playoff.
"I hit a perfect putt perfect speed just to make the playoff," Reed said. "It had to be a matter of time before someone was going to make a birdie and I was 0-for-3 hitting the greens in the playoff and that's how it went."
At the second playoff hole, the par-4 16th, Reed again blasted out of a bunker and saved par while Spieth missed a 12-foot birdie putt and O'Hair had a 10-foot birdie chance for the win.
O'Hair's putt lipped out off the right edge and the drama continued.
"I hit the putt I wanted to hit. I hit a great putt there. I hit it right on my line," O'Hair said. "It just wasn't meant to be."
The playoff then went to 17, when Reed again found a bunker, O'Hair missed a long birdie try and Spieth ended matters in fist-pumping fashion.
Spieth's thoughts drifted back to his two-under-par 69 round, in which he sank an 11-foot birdie putt at the par-3 13th, a 32-foot birdie putt at the par-5 14th, rescued par from a greenside bunker at 16 and pitched to six feet at 17 after finding deep rough.
"It was crazy back nine," Spieth said. "Just the scrambling coming in, the par saves... you want to feed off the energy of the crowd."
O'Hair sank four birdies in six holes, the last of them a 29-footer at 16, to reach the playoff with a round of 67, the same as Stenson and one stroke more than Reed needed in his last round.
Moore made the turn two ahead of Spieth with no other rival inside four shots but missed a five-foot par putt at 10. He responded with birdies at 11 and 12, matching Reed and O'Hair, but then Moore missed a seven-foot par putt at the 13th and a 15-foot par putt at 16.
Needing a birdie at 18 to make the playoff, Moore found deep rough and made bogey.
Stenson birdied three holes in a row starting at the par-5 14th and finished with a 67 to stand on 275, but missed a chance to pass reigning Masters champion Bubba Watson for the world number two spot behind McIlroy with a win or solo runner-up effort.
Leading final-round scores Sunday from the US PGA Tour $5.9 million Valspar Championship (USA unless noted, par-71, x- Spieth wins with birdie on third playoff hole):
274 - Patrick Reed 72-68-68-66, Sean O'Hair 66-72-69-67, x-Jordan Spieth 70-67-68-69
275 - Henrik Stenson (SWE) 67-70-71-67
276 - Ryan Moore 69-68-67-72
278 - Troy Merritt 72-69-71-66
279 - Danny Lee (NZL) 72-69-71-67, Luke Guthrie 68-73-70-68, Jason Kokrak 68-73-70-68
280 - Harris English 69-72-74-65, Kevin Na 71-70-73-66, Charles Howell 70-70-72-68, Justin Thomas 67-72-73-68, Brian Davis (ENG) 65-76-70-69, Vijay Singh (FIJ) 69-70-70-71, Daniel Summerhays 70-72-67-71
281 - Nicholas Thompson 67-74-73-67, Cameron Tringale 71-69-73-68, Lee Westwood (ENG) 71-70-71-69, Shawn Stefani 68-72-71-70, Jason Bohn 70-69-72-70, Billy Hurley 69-71-70-71, Derek Ernst 67-70-69-75
282 - Mark Wilson 70-73-72-67, Ian Poulter (ENG) 68-70-75-69, Andres Romero (ARG) 74-69-71-68, Brendon Todd 70-70-73-69, Jason Dufner 70-71-71-70, Sam Saunders 70-72-69-71, Lucas Glover 69-69-72-72, Chad Campbell 70-72-69-71, Nick Taylor (CAN) 70-70-70-72