Luke Donald shot a final-round 66 at Riviera Country Club but could not prevent Steve Stricker from holding on for victory at the Northern Trust Open.
American Stricker claimed a two-shot win over the Englishman with a one-under-par 70 and climbed to the world No.2 ranking at the expense of two-time defending champion Phil Mickelson.
The left-hander needed a top-six finish to keep the rank but could only manage a tie for 45th after a closing 73.
The victory for Stricker continued a remarkable turnaround for the American since losing his PGA Tour card in 2004. He won the tour's Comeback Player of the Year award in 2006 and 2007, won three titles in 2009 and after three tournaments this year has yet to shoot over par.
"It feels great, this means a lot," an emotional Stricker told NBC Sports. "I remember where I was and look at where I am now, it doesn't get any better and I really appreciate it."
Australian Marc Leishman shot the equal-best round of the day, a six-under 65, to soar into a tie for 15th place at seven-under-par.
New Zealand's Tim Wilkinson could only manage a closing even-par round to claim a share of 20th at six-under, while Aussies Robert Allenby and Rod Pampling were a shot further back at five-under.
Stricker had taken a six-stroke lead into the final round near Los Angeles and, 12 months after losing a two-shot lead in the same tournament to Phil Mickelson, a nervy start in Pacific Palisades saw Donald cut the lead to two after just five holes.
Birdies at the eighth and ninth put Stricker back on the right track before both he and his rival birdied the 11th and then bogeyed the 12th, Donald's first dropped shot in 34 holes.
Donald increased the pressure a little more with a birdie at 13 and further still with a four at the par-five 17th to cut the lead to two, but Stricker held his nerve to par the 72nd hole for victory, the Englishman also parring for his third consecutive top-10 finish at Riviera.
"It was hard," Stricker added. "I aged a lot out there today and it was a grind from the get-go."
Halfway leader Dustin Johnson also shot a 66 to claim a tie for third place at 13-under with fellow American JB Holmes, who carded a 67.
Newly-appointed US Ryder Cup vice-captain Paul Goydos shot a 65 to claim a share of fifth place alongside compatriots Steve Marino and George McNeill, as well as Argentina's Andres Romero.