Mickelson had worked most of his career with Rick Smith, whom he credited for helping him win 30 times on the PGA TOUR and three majors. But he has continued to struggle with his long game, particularly the driver, and it was exposed two weeks ago at the Masters when Mickelson finished out of the top 10 for the first time since 1998.
Harmon spent 10 years working with Tiger Woods, starting with him when Woods was an amateur. He retooled Woods' swing after a 12-shot victory in the 1997 Masters, and Woods captured the career Grand Slam at age 24 in 2000, and later became the first player to hold all four professional majors at the same time.
Before that, Harmon was the coach for Greg Norman when he was No. 1 in the world.
Getting Mickelson to No. 1 might be a tall order, mainly because Lefty is chasing Woods, who has such a large lead in the world ranking he likely will be there the rest of the year no matter what else Woods does.
Harmon watched Mickelson on the range for about 10 minutes at the Accenture Match Play Championship at the end of February, and Harmon again watched him briefly at Doral when Smith was not there.
Mickelson and Smith are close friends off the course, and while Mickelson said that relationship would continue, he said it was tough to leave Smith for someone else.
'I feel that now is the time to go in a new direction with Butch Harmon on my long game,' Mickelson said. 'I went to Rick Smith as a friend and asked for his understanding of this decision and he's been very supportive of it.'
Mickelson was tied for the lead going into the final round of the U.S. Open last year at Winged Foot, an opportunity to join Woods as the only players to win three straight majors in the last 50 years. But he hit only two fairways in the final round, none on the back nine, and his tee shot on the 18th sailed so far left that it clattered off trees and a corporate tent. He made double bogey on the last hole and finished one shot behind Geoff Ogilvy.
'It wasn't just that one drive on 18,' Mickelson said earlier this year. 'I missed them through the entire tournament, but that one drive made me look back at the entire tournament to say, 'What's going on here?''
Mickelson said he and Smith were devising a plan to take the left side out of play off the tee, and while he was flawless in winning by five shots at Pebble Beach, his game quickly began to deteriorate at Bay Hill and Doral as he made his way to the Masters.
He failed to break par -- the first time he failed to do that over four rounds at Augusta National -- and tied for 24th at the Masters.
Mickelson is playing the Byron Nelson Championship, the first of three straight tournaments as he starts getting ready for the U.S. Open at Oakmont.
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