Miami - Jason Day sank a 12-foot birdie putt at 17 and rescued par from a bunker at 18 on Sunday to win the PGA Tour's Arnold Palmer Invitational by a single stroke.
The 28-year-old Australian became the first wire-to-wire winner at Orlando's famed Bay Hill layout since Fred Couples in 1992, just weeks before Couples went on to win the Masters.
Day, who rises to world number two with the triumph, hopes to fit himself for a green jacket at the year's first major tournament in three weeks after collecting the trophy from Palmer, an Augusta National legend.
"It means the world," Day said of the victory. "I just ground it out today. It wasn't the best I had but I got it done when I wasn't quite on."
Day fired a two-under par 70 to finish on 17-under 271, defeating American Kevin Chappell by one with Sweden's Henrik Stenson and American Troy Merritt sharing third on 274 after battling Day throughout the final round.
Day collected his eighth PGA victory, his first since last September's BMW Championship and his fourth in a row when leading after 54 holes. But it was intense.
Stenson, Day and Chappell shared the lead at 16-under with five holes remaining, four of them playing among the course's five toughest, and Merritt was only a shot adrift after four back-nine birdies in a row following a double bogey at the ninth.
Merritt blasted in a 43-foot shot from a greenside bunker at the par-3 14th for his fifth consecutive birdie to grab a share of the lead with Day and Chappell at 16-under after Stenson stumbled with a bogey at 14 and another at 16 after finding the water.
Chappell missed a 26-yard eagle putt at the par-5 16th but tapped in for birdie to grab the lead at 17-under.
Day and Merritt each parred 16 then shined at the par-3 17th, Merritt holing a 12-foot chip shot for par and Day sinking a 12-foot birdie putt to match Chappell for the lead.
Chappell had gone into the right rough at 18 and evaded a water hazard but came up short from 25 feet for par, a bogey ending his day at 16-under, one back of Day as the Aussie came to the last tee.
Day found the right rough and then a bunker beyond the green while Merritt's hopes ended when his approach splashed down shy of the green. Day blasted 90 feet out of the sand and sank a four-foot par putt to win, denying Chappell his first PGA victory.
"I survived," Chappell said. "I felt like I handled myself really well. I would like to have that tee shot back again at 18."
Day pitched in from 70 feet for birdie at the par-3 second to seize a three-shot lead early but followed with back-to-back bogeys while Chappell sank a 16-foot birdie putt at the third to match him for the lead.
Day blasted his tee shot at the fifth just 22 yards off the green and sank a six-foot birdie putt but Chappell matched him with a birdie at the par-5 sixth to keep them even.
But Day followed with a bogey at the sixth, finding the water with his second shot, and Chappell sank a six-foot birdie putt at the seize to reach 16-under and lead by two.
Chappell closed the front nine with a bogey while Day put his approach inches from the cup at the ninth and made birdie to reach the turn level for the lead at 15-under.
Within seconds of each other, Day tapped in for birdie at the 12th and Chappell birdied the 13th to stay level and set up the exciting finish.
Leading scores on Sunday after the final round of the PGA Tour's Arnold Palmer Invitational at Bay Hill in Orlando, Florida, (USA unless noted, par 72):
271 - Jason Day (AUS) 66-65-70-70
272 - Kevin Chappell 68-68-67-69
274 - Henrik Stenson (SWE) 67-66-70-71, Troy Merritt 67-69-67-71
276 - Zach Johnson 70-70-68-68
277 - Kiradech Aphibarnrat (THA) 70-69-73-65, Hideki Matsuyama (JPN) 70-69-71-67, Jamie Lovemark 68-68-71-70
278 - Paul Casey (ENG) 68-69-72-69, Francesco Molinari (ITA) 68-72-69-69, Justin Rose (ENG) 68-66-71-73
279 - Ben Martin 71-70-71-67, Adam Scott (AUS) 67-73-70-69, Chris Kirk 68-71-69-71, Smylie Kaufman 69-71-68-71, Derek Fathauer 70-66-69-74
280 - Marc Leishman 67-70-74-69, Brian Harman 69-71-70-70, Emiliano Grillo (ARG) 68-71-68-73
281 - Billy Horschel 72-67-74-68, Chad Campbell 74-68-71-68, Jason Kokrak 70-68-72-71, Patrick Rodgers 70-70-70-71, Chris Wood (ENG) 69-69-71-72, Rob Oppenheim 70-68-71-72, David Hearn (CAN) 71-67-71-72