World number two Phil Mickelson won the Northern Trust Open by two strokes at Riviera Country Club in California.

Mickelson finished 12 under after a final round 70 but was handed the title after main rival Jeff Quinney imploded on the back nine.

Open champion Padraig Harrington and Ryder Cup team-mate Luke Donald both shot 68 to finish in a tie for third.

It was a tournament the left-hander had long coveted, having lost in a play-off after bogeying the 18th 12 months ago, while at the FBR Open two weeks ago, Mickelson had a one-stroke lead but JB Holmes birdied the final hole to force a play-off which he won on the first extra hole.

This time, Mickelson minimised his mistakes and took a three-shot lead to the final hole.

"It is pretty cool," Mickelson said. "I've wanted to win here for a long time. It was a tough fight with Jeff. He played really well.

"I had some solid shots on the back nine and Jeff had a couple of three-putts to give me the lead. I was able to not make any mistakes and hang on to win.

"I felt I had the tournament won last year and I bogeyed 18. I didn't want to get ahead of myself. I wanted to try to play each shot smart coming down the stretch and not get too emotional."

Mickelson began the day with a one-stroke advantage over Quinney but after nine holes he had been overtaken by his compatriot.

The left-hander had gone three ahead after a birdie at the par-five opening hole was then followed by Quinney bogeying the third after missing a seven-foot putt.

However, a run of three birdies in four holes from the sixth, coupled with a Mickelson bogey at the ninth, turned things around.

Two successive birdies from Mickelson put him ahead again even though his rival picked up a shot at the 11th but then four bogeys in five holes handed the title to the three-time major winner.

Mickelson earned USD1.116 million for his first victory of the season and the 33rd of his career.

"I thought in the middle of the round, he made some incredible putts that made for a very difficult day," Mickelson added.

"I was fortunate to be able to respond to those with a birdie on 10 and 11, and that gave me a little bit of momentum."

Quinney attributed his back nine trouble to miscalculations with the putter.

"Obviously just put a little too much pressure on the putter on the back nine," Quinney said.

Englishman Donald was pleased with the start he has made to his PGA Tour career.

"It's my first event on the PGA Tour and to come out and to play solidly all week, it's very encouraging," Donald said. "It's just showing the work I've been doing over the off season is starting to pay off."

Collated final round scores & totals (USA unless stated, par 71):

272 Phil Mickelson 68 64 70 70

274 Jeff Quinney 69 67 67 71

277 Luke Donald (Eng) 68 71 70 68, Padraig Harrington (Irl) 69 69 71 68

278 Ryuji Imada (Jpn) 71 69 70 68, Scott Verplank 68 69 71 70

279 J.B. Holmes 74 66 69 70, Robert Allenby (Aus) 70 66 75 68, KJ Choi (Kor) 65 73 71 70, Stuart Appleby (Aus) 69 70 69 71

280 Steve Stricker 71 69 71 69, Chad Campbell 67 70 73 70, Mark Wilson 70 70 69 71

281 Adam Scott (Aus) 73 69 70 69, Steve Flesch 71 71 68 71, Matt Kuchar 73 71 70 67, Bubba Watson 71 68 71 71, Charlie Wi (Kor) 70 68 71 72, Joe Durant 71 70 69 71, John Rollins 68 70 69 74, Jason Gore 71 72 71 67

282 Vaughn Taylor 67 70 71 74, Lucas Glover 72 69 70 71, David Toms 71 68 72 71, Kevin Sutherland 70 69 73 70, Peter Lonard (Aus) 69 70 74 69, Paul Casey (Eng) 73 70 69 70, Nathan Green (Aus) 72 70 70 70, Marc Turnesa 75 70 67 70, D.J. Trahan 70 74 66 72

283 Hunter Mahan 68 74 70 71, Tag Ridings 75 68 70 70, Brandt Jobe 71 68 71 73, Angel Cabrera (Arg) 68 73 70 72, Fred Couples 70 70 72 71

284 Brad Adamonis 72 71 69 72, Pat Perez 69 72 71 72, Bart Bryant 74 69 71 70, Jeff Overton 74 69 70 71, Alex Cejka (Ger) 68 72 73 71, George McNeill 72 69 71 72, Vijay Singh (Fij) 71 72 71 70, Bill Haas 72 71 72 69

285 Rory Sabbatini (Rsa) 72 67 74 72, Billy Mayfair 68 69 74 74

286 Scott McCarron 72 65 76 73, Zach Johnson 72 67 71 76, Tom Pernice Jnr. 72 72 68 74, Brian Bateman 70 70 76 70, Toru Taniguchi (Jpn) 72 71 71 72, Aaron Baddeley (Aus) 73 70 74 69, Stephen Marino 69 70 71 76, Sergio Garcia (Spa) 74 71 69 72, Craig Barlow 69 74 69 74

287 Kevin Na (Kor) 66 76 73 72, Ben Crane 70 74 73 70, Fredrik Jacobson (Swe) 72 73 72 70, Charles Howell III 71 70 74 72

288 Dustin Johnson 68 73 69 78, Michael Allen 75 70 73 70, Cody Freeman 70 74 72 72

289 Kenny Perry 72 73 70 74, Cameron Beckman 74 70 72 73, Ben Curtis 70 71 76 72, Shigeki Maruyama (Jpn) 71 74 74 70, Rocco Mediate 75 70 70 74, Ryan Moore 72 71 71 75

290 Mathew Goggin (Aus) 73 71 72 74, Kevin Streelman 75 69 74 72

291 Will MacKenzie 71 73 75 72, Dean Wilson 71 72 74 74, Bo Van Pelt 71 74 72 74, Briny Baird 71 74 70 76, Fred Funk 74 70 71 76

292 John Daly 69 74 73 76, Eric Axley 71 72 78 71, Carl Pettersson (Swe) 70 74 74 74

293 Chez Reavie 73 71 71 78