Bill Haas rolled in a 45-foot birdie putt at the second playoff hole on Sunday to win the Northern Trust Open and deny Phil Mickelson a second US PGA Tour title in as many weeks.
Mickelson, who was coming off a storming victory at Pebble Beach last Sunday, had led or shared the lead here after each of the first three rounds.
He and Keegan Bradley, who shared the overnight lead, made Haas work overtime by sinking birdie putts at the final hole of regulation to force the three-man playoff, but it was Haas who came through on the second playoff hole - Riviera Country Club's often dramatic 315-yard, par-four 10th.
Mickelson put his tee shot in the right rough short of the green. Bradley was in the right greenside bunker while Haas was in the back left rough.
Haas pitched safely to the middle of the green. Mickelson's shot out of the rough rolled through the green and into the back bunker while Bradley fired out of the sand to the back fringe.
Haas sank his long birdie putt, then waited tensely as Mickelson and Bradley tried in vain to extend the playoff.
"Bill hit a tremendous putt," Mickelson said. "That's going to do it."
Haas said he wasn't really expecting his putt to drop.
"I never expect to make a 40-footer, especially in that situation," he said. "That was a little bit of luck involved, but I felt like I put a good roll on it."
Haas had been the first in the clubhouse on seven-under 277 after a two-under par 69.
He had seized a one-shot lead with a birdie at the par-five 17th. His lead looked safer after neither Mickelson nor Bradley could take advantage of the 17th, Mickelson's long birdie putt stopping an inch short.
But the overnight co-leaders responded at the last hole of regulation.
Mickelson, who had struggled all day on Riviera's testing greens, rolled in a 26-footer from the back fringe to complete his even-par 71.
Moments later Bradley made his own 13-foot birdie putt for his 71 and headed with Mickelson and Haas back to the 18th - which they all parred to open the playoff.
"I knew Phil was going to make that putt," said Bradley, who was named the US tour's Rookie of the Year after a 2011 campaign that included a major title at the PGA Championship.
"Phil is too much of a gamer to not make that putt," Bradley added.
"I kept fighting," said Mickelson, who led by as many as two during the round but also gave up the lead with back-to-back bogeys at eight and nine and again with three-putt bogeys at 14 and 15.
"I was giving away shots and was trying to let it go and move on and see if I could capture one," Mickelson said. "I finally got one to go on 18. It felt great."
Haas wasn't surprised to be in a playoff - he had already headed to the range expecting one when he heard the cheers from the 18th green.
"Secretly I was hoping they didn't, but Phil just won his 40th event. Keegan won a major last year, so I expected them to make it," Haas said.
Haas claimed his fourth US PGA Tour title, and his first since he won last year's Tour Championship - where he also captured the FedEx Cup playoff title and its $10 million bonus.
Spain's Sergio Garcia was the unlikely leader of a group of four players sharing fourth place on five-under par 279.
Garcia, who started the day nine adrift, carded a seven-under 64 - the best round of the tournament - that included two eagles and five birdies.
He was joined on 279 by Jimmy Walker (69), Australian Jarrod Lyle (70) and Dustin Johnson (71).
World number one Luke Donald endured a difficult day, shooting a seven-over 78 that included eight bogeys, six of them in a row from the ninth.
He blamed his inability to get to grips with Riviera's greens, and said he wasn't hitting it too badly heading into his defence of the World Golf Championships Match Play Championship in Arizona starting on Wednesday.