"I am such an idiot," Mickelson fumed afterward, furious at himself and humiliated.
From there, he pretty much disappeared for a while, then returned only to wander aimlessly through the last part of the season, showing up in body but not spirit at the Ryder Cup, where the Americans got stomped.
Now, however, Mickelson is an idiot no more. Indeed, he arrives at Oakmont Country Club riding a wave of success, fresh from an impressive and encouraging win a month ago at the Players Championship.
Besides the confidence-builder of winning in one of the strongest fields of the year, Mickelson's rock-solid performance was seen as proof that he was making quick progress under a new swing coach, Butch Harmon, the same man who rebuilt Tiger Woods' swing before his "Tiger Slam" in 2000.
"Butch, the first of many," Mickelson wrote on the flag from the 18th hole at TPC Sawgrass, which he sent to Harmon as a souvenir.
"You're just seeing the tip of the iceberg," said Harmon. "This is just three weeks into the process. He's going to get a lot better."
How much better, if any, Mickelson has gotten since then is a mystery.
In his only other event since, Jack Nicklaus' Memorial Tournament a week ago, Mickelson withdrew midway through his first round, complaining of an aggravated left wrist.
He had intended to play this weekend's Stanford St. Jude Championship, but he ended up withdrawing before the start, preferring to rest his wrist for the Open.
Although Mickelson has won the Masters twice ('04, '06) and the PGA Championship once ('05), the Open has remained the one major on U.S. soil that has eluded him. Four times he has finished second: last year at Winged Foot (Geoff Ogilvy won), in '04 at Shinnecock (Retief Goosen), in '02 at Bethpage (Woods) and in '99 at Pinehurst No. 2 (Payne Stewart). When the Open was last at Oakmont, in 1994, Mickelson finished tied for 47th.
Assuming he and his wrist are ready to go, Mickelson's pursuit of the title and the silver trophy won't get any easier at the notoriously difficult Oakmont, which is hosting its eighth Open, more than any other club in the country.
At the Memorial, Mickelson liked his chances this week.
"I've played well in a tournament that theoretically shouldn't be my strength, shouldn't be the tournament that I play best at," he said, referring to his reputation for run-and-gun golf and the Open's reputation as a survival test. "I feel it's a tournament that I should be able to win, that I can win, but I haven't done it yet. I relish the chance."
Since the last Open at Oakmont, the club has removed upward of 4,000 trees as part of a restoration project to return the course to its original look and feel. Whether Oakmont watchers like or hate the changes, they all agree it has made for a significant transformation of the course as they knew it.
"Without the trees, it had a very cool look," said Mickelson. "You saw a lot more of the course. You saw a lot more of the fescue, the rough, the fairway, the sand, a lot more colors on the course, character on the course," said Mickelson. "I just thought it looked great."
Because of the severe slopes, the greens at Oakmont are more difficult to putt than even those at the home of the Masters, Augusta National - a fact Mickelson expects the U.S. Golf Association to only make worse, or better, depending on your perspective.
By far, the hole that is getting the most hype is the eighth, a par 3 that will play 288 yards this week, making it the longest 3-par in the history of the championship.
After trying four clubs there, Mickelson expects to hit 3-wood, maybe a hybrid. "It's a tough hole, really tough," he said.
If one thing is certain, if Mickelson comes to the 72d hole in the lead next Sunday, don't expect him to reach for his driver.
Contact staff writer Joe Logan
at 215-854-5604 or email@example.com. Read his recent work at http://go.philly.com/joelogan.