Mickelson (42) whose recent form slump sent him spinning out of the world's top 20 for the first time since 1996, played like a superstar reborn as he ripped out 11 birdies in a foot-perfect round which should have yielded only the sixth 59 in PGA Tour history.
Mickelson looked on in disbelief as his 25-foot birdie putt at his final hole, the ninth, rolled around the rim and back out at him.
"The last six feet it was right on glide slope," he said. "It should've been right in middle. You don't have chances to shoot 59 often. To have that putt on line, I'm kind of mortified it didn't go in."
Mickelson's only previous 60 came in the second round of the Phoenix Open in 2005, when he went on to win the tournament for the second time.
The vast improvement in his driving and putting yesterday – Lefty had 12 one-putt greens – gave him a head-start in his race for a third title at Scottsdale.
Harrington's 64 was a magnificent effort on his debut in Phoenix, where he can give full vent to his natural aggression.
Like Mickelson, the Dubliner drove his ball prodigious distances in the desert air, while his short game and putter were white-hot.
He sank an impressive series of medium and long-range putts, including one from 26 feet at his opening hole, and even pitched in from a greenside bunker for birdie at 14.
Harrington made a comfortable par on his first appearance in front of 30,000 fans crammed into that bubbling cauldron of noise and nervous excitement, the par-three 16th hole.
He planted his tee shot in the heart of the green and two-putted from 38 feet.
Vijay Singh withdrew from the tournament yesterday.
A back injury was cited in the statement issued on his behalf by the Tour, but the Fijian was never likely to play after admitting he used a deer antler spray said to contain a banned substance.
Singh's peers are stunned any professional would take a supplement without ensuring it contains no substances that contravene the anti-doping programme established in 2008.
"I think we should check people for mental problems if they're taking deer antler spray," said Masters champion Bubba Watson.
"It's sad that people would put weird stuff in their body not knowing what it's going to do to them."
Though there is no test to detect the banned IGF – 1 (Insulin-like Growth Factor) supposedly contained in the spray, Singh has admitted using it several times each day since purchasing it last November.
The regulations state golfers may be found in violation of the rules for "admitting to any conduct that violates the programme".
The PGA Tour specifically banned deer antler spray 18 months ago, issuing a circular to all members advising of its illegality.
However, without analysis of the actual spray Singh used, there's no proof he ingested a banned substance as the manufacture of deer antler spray is not regulated.
Meanwhile, Irish golf has lost one of its true characters with the death after a short illness of Jim (JD) Murphy from Kilkenny, father of European Tour professional Gary.
The former investment broker was a great sportsman himself and coached the juvenile section of Kilkenny Golf Club for many years.
Peter Lawrie and Damien McGrane last night led the tributes to the 68-year-old.
"This is a very sad day," said Lawrie. "He was a fine gentleman and always very supportive and encouraging."
McGrane added: "JD was a lovely fellow. We extend our deepest sympathy."
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