FORT WORTH, May 26, 2014 (AFP) - The Australian rolled in a seven-foot birdie putt at the third playoff hole for the victory, cementing his number one status in style.
He was playing as the world's top player for the first time since taking over from injury-idled Tiger Woods on Monday.
The 2013 Masters champion's hopes of maintaining the top spot took a hit with a first-round one-over 71 at Colonial Country Club in Fort Worth, Texas on Thursday.
But he clawed his way back, and had gone into Sunday's final round of the $6.4 million tournament tied for 11th but just two shots off the lead.
"This is a really special week for me," Scott said. "It was, no matter what happened here. But to kind of find my way back into this tournament, around this golf course -- it's a real honor to win here. It's a beauty."
Henrik Stenson, the world number three from Sweden who was vying to move past Woods and Scott to seize the top ranking, still had a chance after finishing tied for seventh earlier on Sunday in the European PGA Championship at Wentworth won by Rory McIlroy.
Based on Stenson's finish, Scott needed a top-13 finish to stay atop the rankings.
Scott rolled in a 40-foot birdie putt at the par-four 14th, his seventh birdie of the day giving him a share of the lead at nine-under par along with David Toms.
Toms then bogeyed the 10th to leave Scott alone atop the leaderboard, but Dufner, the 2013 PGA Championship winner, notched the last of his five birdies at the 72nd hole of regulation, draining a 25-footer to get to nine-under tied for the lead with Scott, who couldn't find another birdie in his last four holes.
"I'm glad I hung in there and finally got one to fall inside on 18," Dufner said.
Both Dufner and Scott signed for four-under-par 66s in the final round for nine-under 271.
They shot matching pars at the first playoff hole -- the par-four 18th-- and both birdied the second playoff hole, Scott sinking a clutch 14-footer from the fringe at 17 to put the pressure on Dufner to make his four-footer.
They returned to 18 for the third playoff hole. Both were in the fairway, but Dufner's second shot left him a 35-foot putt for birdie. When he rolled it past, Scott stepped up and made his.
American Nicholas Thompson posted a 66 and Sweden's Freddie Jacobson carded a 67 to share second on 272.
- 'Texas Grand Slam' -
Scott, who returned to Colonial for the first time since 2011, added an unprecedented item to his resume: a career sweep of all of the US PGA Tour titles in Texas.
He won the Houston Open in 2007, the Byron Nelson Championship in 2009 and the Texas Open in 2010.
The list of players who have fallen one shy of the so-called Texas Grand Slam includes such notable names as Ben Hogan, Sam Snead, Byron Nelson, Arnold Palmer, Nick Price and Phil Mickelson.
"I was determined," said Scott. "I wanted to have a chance at this one because I really wanted to win them all here in Texas."
Scott also improved his perfect record in playoffs on the US PGA Tour. He has won all three that he has contested -- including at the 2013 Masters, where he beat Angel Cabrera at the second playoff hole.
Leading scores after Sunday's final round of the $6.4 million US PGA Tour's Colonial tournament (x-won playoff, USA unless noted, par-70):
271 - x-Adam Scott (AUS) 71-68-66-66, Jason Dufner 67-69-69-66
272 - Nicholas Thompson 69-68-69-66, Freddie Jacobson (SWE) 67-71-67-67
273 - David Lingmerth (SWE) 72-69-66-66, Ryan Palmer 69-69-68-67, Brendon Todd 69-69-67-68, John Senden (AUS) 71-68-66-68, David Toms 72-66-65-70
274 - Michael Thompson 73-66-69-66, Jimmy Walker 67-68-69-70, Kevin Chappell 68-73-63-70, Hideki Matsuyama (JPN) 69-70-64-71
275 - Dustin Johnson 65-70-74-66, Graham DeLaet (CAN) 69-70-68-68, Jordan Spieth 67-69-70-69, Bo Van Pelt 67-68-70-70, Brian Davis (ENG) 68-67-70-70, Chris Kirk 73-64-67-71, Chris Stroud 70-64-69-72
276 - David Hearn (CAN) 67-69-74-66, Bud Cauley 70-69-69-68, George McNeill 68-72-68-68, Ben Martin 70-68-69-69, Bill Haas 70-68-69-69, Russell Knox (SCO) 71-70-66-69, William McGirt 72-67-67-70, Tim Clark (RSA) 67-68-69-72, Marc Leishman (AUS) 69-68-67-72