Los Angeles - Australia's Marc Leishman fired eight birdies in a seven-under par 65 on Sunday to win the PGA Tour title at Torrey Pines by one stroke from overnight leader Jon Rahm.
Leishman started the day four shots behind Spain's Rahm, but his storming run on Torrey Pines' South Course gave him a 15-under total of 273.
Rahm, meanwhile, fired a two-under 70 for 274, two shots in front of American Brandt Snedeker and Rory McIlroy - the Northern Ireland star who could have regained the world number one ranking with a victory.
"Playing well helps," said Leishman, who has come from behind in all five of his PGA Tour victories.
"I didn't actually hit it that well off the tee today, so I don't know what the knack is. Putting, always, you're not going to win tour events if you're not putting well.
"I putted probably as good as I've ever putted today," added Leishman, who had five birdies on the front nine.
He drained par-saving putts at the 12th and 14th, and rebounded from his only bogey of the day at 17 with a birdie at the last that proved enough for victory.
Leishman's victory came on Australia Day - also the same day that fellow Aussie Lucas Herbert claimed his first pro victory at the Dubai Desert Classic.
McIlroy and Rahm struggled in the final group, Rahm playing his first five holes in four-over with two bogeys and a double-bogey.
An eagle and four of his five birdies on the back nine - including three birdies to end his round - weren't enough to compensate.
McIlroy, meanwhile, began bogey-bogey on the way to 69.
Tiger Woods missed the green on his opening approach and began with a bogey but dropped his approach inches from the cup at the second to set up a birdie and added another tap-in birdie at the par-5 sixth to pull within three strokes of the lead.
The 15-time major champion finished with four birdies in a two-under 70 that left him tied for ninth on 279.
He remains in search of a record 83rd career PGA Tour victory - having tied Sam Snead's mark at the Zozo Championship in Japan in October.
As he came off the course Woods learned of the death in a helicopter crash of Kobe Bryant - the NBA great who started his pro career the same year as Woods.
"People were yelling, 'Do it for Mamba.' Now I understand," Woods said.
Leading scores after Sunday's final round of the PGA Tour Farmers Insurance Open at Torrey Pines in La Jolla, California (USA unless noted, par-72):
273 - Marc Leishman (AUS) 68-72-68-65
274 - Jon Rahm (ESP) 68-71-65-70
276 - Brandt Snedeker 69-67-72-68, Rory McIlroy (NIR) 67-73-67-69
277 - Tom Hoge 71-71-67-68
278 - Bubba Watson 67-73-69-69, Patrick Reed 69-69-70-70, Tony Finau 70-70-68-70
279 - Max Homa 73-68-71-67, Patrick Rodgers 70-69-72-68, Beau Hossler 72-66-73-68, Charley Hoffman 69-74-71-65, Tiger Woods 69-71-69-70, Harry Higgs 70-68-69-72
280 - Maverick McNealy 71-71-69-69
281 - Jason Day (AUS) 73-67-72-69, Keegan Bradley 66-72-73-70, JB Holmes 68-69-71-73, Kang Sung (KOR) 69-71-67-74, Cameron Champ 71-68-68-74