The way he surged into a share of the lead Saturday, it looked like he borrowed a page from Tiger Woods, the man he's trying to catch in the record book.
And when a torturous day at Winged Foot was in the books, Mickelson shot a 1-under 69 and was on the verge of joining Woods in a small chapter of golf history as the only players to win three straight majors on the schedule.
All that stands in the way is 18 holes and an unheralded Englishman, Kenneth Ferrie, whose three-putt bogey from the fringe on the 18th hole gave him a 71 and dropped him into a tie with Mickelson at 2-over 212, the seventh time in the last 11 rounds at a major that Lefty was atop the leaderboard.
Woods, of course, can't do anything about it because he missed the cut.
Mickelson sat next to the U.S. Open trophy in a television interview. It was close enough to touch, but he kept his hands to himself.
'I've got one round to go, 18 holes, and there's a lot of guys right there, a lot of good players that are making pars and fighting, just like I'm trying to do,' Mickelson said. 'I'm not thinking about those past tournaments. I'm trying to just play one more good round.'
It was the first time the 54-hole lead was over par at the U.S. Open since 1974, known as the 'Massacre of Winged Foot,' when Tom Watson led at 3-over 213 and Hale Irwin wound up winning at 7-over 287. That was the year Winged Foot got its reputation as one wicked test of golf, and it sure lived up its reputation on this steamy Saturday.
'One time a year, we get tested like this. And I love it,' Mickelson said. 'I love being tested at the highest level of the most difficult and sometimes ridiculous golf course setups we'll ever see. I love it because I get to find out where my game is at, where my head is at, and it really challenges me as a player.'
As for the challengers on the course?
Ferrie is a 37-year-old playing only his fourth major, and his first U.S. Open. He was surprisingly steady except for a flew blips on the back nine, when he took bogey from the bunker on the par-3 13th and ran his birdie putt from the fringe on the 18th some 6 feet past the hole, missing the par attempt badly.
'I just heard Phil saying that it's kind of the biggest test in golf of every part of your game,' Ferrie said. 'So far I've ... I wouldn't say passed yet, but I'm well on my way to getting a decent grade.'
Geoff Ogilvy of Australia, who won the Accenture Match Play Championship in February, made two straight bogeys on the back to wreck an otherwise solid round, finishing with a 2-over 72 that left him one shot out of the lead.
The group at 5-over 215 all had their moments, good and bad.
-- Three-time major winner Vijay Singh had to scramble for bogey on the 13th and holed a 30-foot par putt late to secure a 70.
-- Ian Poulter of England had a chip roll back to his feet from short of the 18th, making bogey to spoil his round of 70. He only has three shots to make up, far less daunting than last year's British Open, when he started the last round nine shots behind Woods and made up only one.
'I'm knocking on the door, and I feel very, very happy,' Poulter said.
-- Steve Stricker held on to his tenuous lead for eight holes until he started missing fairways and limped home to a 76.
-- Colin Montgomerie dropped five shots on his first four holes, then steadied himself for a 75 that kept alive faint hopes of a first major championship.
'That was a disaster,' Monty said of his start. 'Five over to finish was a hell of an effort. I pat myself on the back tonight. The last 14 holes were good.'
The last hole was awful for Padraig Harrington.
The Irishman needed a birdie to catch Mickelson, but made a mess of it. He barely made contact out of the deep rough, moving the ball only about 15 yards into the fairway. Once he got out of a greenside bunker, he three-putted for a triple bogey that sent him spiraling down the leaderboard with a 74, in the group at 6-over 216 with Mike Weir (71) and Jim Furyk (74).
Weir hit what he thought was his best shot on the 18th, only to see it roll off the green and into a bunker. From there, he blasted over the green and couldn't get up and down, ending with a double bogey.
Mickelson was immune to such struggles on the back nine.
He holed a 6-foot birdie putt on the 14th hole and a slippery 15-footer on the 16th that sent the New York gallery into a frenzy, one of the few times all day they had reason to unleash their unbridled support of their beloved Lefty. Mickelson's 10-foot birdie try on the 18th ran 5 feet by the cup, but he made that for par and walked off the green with a tip of the cap.
Ten players were separated by four shots, with four of them having won majors. But the focus is squarely on Mickelson.
'Somebody told me today on the course I was 'the man,'' Ferrie said. 'I guess Phil is a bigger man.'
New Yorkers fell in love with Lefty at Bethpage Black when he was a sympathetic figure in a losing battle with Woods at the 2002 U.S. Open. He broke their hearts two years later at Shinnecock Hills, tied for the lead until a double bogey on the 71st hole. Even after his breakthrough at the 2004 Masters, the connection between Mickelson and New York was strong.
Now, he has a chance to give them something to really cheer.
'He's got the opportunity of doing what Tiger did, winning three majors in a row,' Montgomerie said. 'That's a big feat.'
Mickelson climbed into the lead the way Woods has done so many times, and he credits his play to having studied Winged Foot as if he were cramming for a major exam.
'I have notes on every shot, from drive to iron to putt to chip,' Mickelson said. 'Knowing where I can and can't go and how the slopes can help me or hurt me, that's allowed me to hang in there and make par, par, par and occasionally birdie.'
It has put him atop the leaderboard with one round to go, and Woods nowhere to be found except in the record books.