The big-hitting American, who closed with a 3-under 69, got the better of six other players - including Londoner Brian Davis - who, like him, had all began the final round hoping to record the first Tour title of their careers.

Instead Johnson sunk an eight-foot birdie putt on the final hole at Verona, near New York, to edge out seasoned veteran Australian Robert Allenby by one shot.

Allenby, seeking his fifth victory and first since 2001, was denied when his 12-foot last-gasp putt for a birdie to tie with Johnson stopped just short.

Home hopes Tag Ridings, Kyle Thompson and Jeff Overton and Australian Jason Day were among those who ran out of steam in the closing stages.

Davis hit a 74 to finish on a five-under 283 and tie for 15th - having started the day third.

Johnson seemed a little dazed by this early success on the tough US PGA Tour.

When asked how he felt about his first Tour victory, he said: "I'm not really sure. Hasn't quite sunk in yet, so I don't really quite know what's going on yet.

"Obviously it's a great feeling. I feel like I've worked real hard the last month to get my game in shape to, you know, be in the position to win a tournament, so I'm very excited."

Johnson said part of the reason for his hard work in recent weeks was a pow-wow he had with his coach. They were looking for reasons why his performances had dipped after a solid start in the early part of 2008.

"We just sat down and just kind of -- I don't know, it's kind of hard to explain. Just I knew I had to focus a lot more, especially on my practice, and you know, the things we were working on in my posture and my setup and the takeaway. Just made sure I worked on them every day.

"I also worked a lot harder on my short game and my putting, which I had been doing. It paid off, because I made a lot of good putts coming down the stretch on Sunday.

ALL THE FINAL ROUND SCORES
(USA unless stated, par 72):

279 Dustin Johnson 72 68 70 69

280 Robert Allenby (Aus) 71 68 71 70

281 Robert Garrigus 72 72 68 69, Mathew Goggin (Aus) 71 70 71 69, Davis Love III 75 70 66 70, Woody Austin 74 69 69 69, Ryuji Imada (Jpn) 72 71 69 69, Steve Allan (Aus) 68 74 70 69, Charles Howell III 71 68 69 73

282 Charles Warren 73 71 67 71, Pat Perez 71 72 69 70, Jeff Overton 67 69 73 73, Joe Ogilvie 75 69 68 70, Nick O'Hern (Aus) 71 72 71 68

283 Brian Davis (Eng) 71 69 69 74, Vaughn Taylor 75 69 69 70, Mark Hensby (Aus) 70 69 72 72, Steve Elkington (Aus) 73 71 70 69

284 J J Henry 74 72 71 67, Bo Van Pelt 70 73 71 70, Jason Day (Aus) 69 69 71 75

285 George McNeill 73 71 72 69, Brad Elder 71 69 72 73, James Driscoll 76 71 68 70

286 Kevin Stadler 71 75 69 71, Ryan Moore 74 74 69 69

287 Richard Johnson (Wal) 76 71 69 71, Brandt Jobe 71 75 71 70, Frazar Harrison 72 70 72 73, Tag Ridings 69 68 71 79, John Senden (Aus) 73 71 73 70, Michael Allen 68 74 74 71, Sean O'Hair 73 71 70 73, Carlos Franco (Par) 69 78 70 70, Troy Matteson 70 73 71 73

288 Kent Jones 70 74 72 72, Patrick Sheehan 72 76 68 72, Steve Marino 75 73 68 72, Nathan Green (Aus) 73 75 70 70, Kyle Thompson 71 69 69 79, Briny Baird 70 72 71 75, Tim Wilkinson (Nzl) 73 71 74 70

289 Joe Durant 71 75 71 72, Chad Collins 72 75 72 70, Scott Sterling 70 76 72 71, Casey Wittenberg 74 74 72 69, Todd Demsey 72 71 75 71, Olin Browne 72 71 75 71, Tommy Gainey 71 74 70 74

290 Bob Sowards 74 69 72 75, Kevin Na 72 71 75 72, Michael Bradley 75 73 70 72, Mathias Gronberg (Swe) 74 74 71 71, Shane Bertsch 75 71 69 75

291 Paul Claxton 70 72 71 78, Y. E Yang (Kor) 74 72 72 73, Bob Estes 72 74 72 73, Rich Beem 74 74 69 74, Carl Pettersson (Swe) 73 73 73 72, Peter Lonard (Aus) 78 67 73 73

292 Brett Rumford (Aus) 73 71 74 74, Cody Freeman 74 72 74 72, Steve Flesch 74 73 73 72, Tom Pernice Jnr. 72 73 69 78, Johnson Wagner 73 73 70 76

293 Nick Watney 77 70 73 73, Parker McLachlin 73 75 72 73

294 Brad Adamonis 74 73 72 75, Joey Sindelar 77 71 72 74, Dicky Pride 76 71 71 76, Ryan Armour 74 74 70 76